Cold drawn high-orientation multilayered film and process for manufacture of said film

ABSTRACT

A high-orientation multilayered film incorporates at least one cold drawn, highly oriented resin layer excellent in mechanical strength and suitable mainly for use as packaging material. Because of its specific stratal construction which is highly adaptable to afford a wide variety of specific functions, the composite film is suitable for manufacture of thermally shrinkable films which excel in transparency and in ability to shrink rapidly particularly at low temperatures. Also disclosed is a process for drawing at specific low temperatures at high expansion ratios the aforementioned multiplicity of resin layers either all by themselves or in conjunction with layers of other resins by utilizing the cold drawability of the aforementioned resin layers excelling in mechanical strength.

This is a Division of application Ser. No. 548,018 filed Nov. 1, 1983,which is in turn a continuation of application Ser. No. 316,101 filedOct. 28, 1981, now abandoned, which is in turn a divisional ofapplication Ser. No. 103,944 filed Dec. 14, 1979, now abandoned.

BACKGROUND OF THE INVENTION

Packages formed with films are manufactured by a good number of methodswhich utilize to advantage the characteristics of the films such as thebag sealing method, twist wrapping method, thermal shrink wrappingmethod, cohesive wrapping method by use of specific films represented bySaran Wrap (product by Asahi-Dow Limited), stretch wrapping method, skinpacking method intended to provide intimate adhesion between the filmand its contents by virtue of heat and vacuum, vacuum packing methoddesigned to produce tightly drawn packages by means of evacuation andthe like. These methods require respective wrapping characteristics. Foreach packaging method, therefore, it is important to select a film whosebasic material, composition, form and characteristic attributes bestsuit the wrapping characteristics of the particular method employed.

The films of this class, depending on various uses found therefor, arerequired to possess a broad spectrum of properties befitting anassortment of factors including the kind of article to be wrapped, thecondition of preservation of the wrapped article and the like. Recently,owing to increasingly more exaction of special properties, the practiceof using composite films formed of a multiplicity of layers of varyingproperties has come to find favorable acceptance. The multilayered filmwhich is produced by preparing a substantially unoriented film ororiented film, then melt extruding other resin into a film andlaminating the freshly extruded film with the former film offers oneexample.

A film of improved heat sealing property produced by fusion laminatingan unoriented polypropylene layer of the cast method (called as "C.PP")or an oriented polypropylene layer (O.PP) with a layer of other resinand a film coated with a vinylidene chloride type latex or solvent toacquire a barrier property (called as "K-coat film") are other examples.These and other various types of films and their various combinationsare selected to suit numerous applications.

On the other hand, a coextruded film which is produced by meltingseveral different resins in some extruders and, with the aid of amultilayered die, joining the respective extruded sheets of the resinswithin the die, fusing the joined resin sheets, extruding the resultantcomposite sheet and cooling it into a film or sheet is widely known.

The optimum extruding and stretching conditions required for successfulconversion of these multilayered sheets into highly oriented films varyfrom one to another of the resins used in the component layers making upthe composite sheets. Owing to this variability of the optimal extrudingand stretching conditions, the films under production suffer detestablephenomena such as inconsistent wall thickness, streaks, puncture,rupture, layer separation, and blushing due to coarsened interfaces, andthe properties acquired by the produced films differ from those thefilms are expected to acquire. Elimination of these difficulties hasturned out to be an extremely difficult task.

This invention aims to provide films which are usable for variouspurposes, particularly films which satisfy the purpose of shrinkwrapping. Now the films of the kind produced by this inventionspecifically for the purpose of shrink wrapping will be described belowby way of illustration of the invention.

Generally, the shrink wrapping method, on the principle of full use ofthe heat shrink property of a film which has been stretched to acquire aspecifically set orientation, comprises the steps of looselypre-wrapping or sealing a given article subjected to wrapping so as toenclose the article with a film and, thereafter, exposing the film to aheat medium such as current of hot air, infrared ray, hot water, and thelike and thereby causing the film to shrink and come into tight contactwith the overall contour of the article. This method is characterized bythe fact that the produced package has beautiful appearance enough toadd to the commodity value of the wrapped article, keeps the contentshygienic, permits shoppers to examine the quality of the contents by thesenses of vision and touch, keeps the contents tightly in position nomatter whether the article consists of a plurality of pieces or a singlepiece and provides the contents with ample protection against vibrationsand impacts. Compared with the stretched wrapping method which is usedextensively as in supermarkets, the shrink wrapping method enjoys highspeed of wrapping work. The shrink wrapping method is now findinggeneral acceptance with ever increasing impetus in the industrialpackaging operations which generally involve articles too voluminous andheavy to be advantageously handled by the stretch wrapping method alone.This fact has come to attract keen attention of the industry.

Articles which are too irregular in contour to be packaged by thestretch wrapping method and articles which do not permit use of rigidauxiliary containers such as trays can be advantageously packaged bythis shrink wrapping method. Further, this method enjoys the advantagethat the article can be packaged with more tightness than by any othermethod. Despite these advantages, this method still has the disadvantagethat the film wrapped around the article must be heated thoroughly untilit amply shrinks.

The film currently used more extensively by this shrink wrapping methodis a drawn film of plastic polyvinyl chloride (hereinafter referred toas "PVC") resin. The popular use of this film is ascribed to the film'soutstanding ability to produce high degree of heat shrinkage at arelatively low temperature and provide advantageous shrink wrapping in awide range of temperatures. On the other hand, this film is deficient inheat sealing property, preservability (due to inclination toward lose oforientation by the action of a plasticizer), and moistureproofness. Itfurther entails hard problems such as the impairment of hygiene by theplasticizer, emission of chlorine type gas and other noxious gasesduring the fusion of film by the heated wire, liberation of corrosivenoxious gases during the combustion of film in the incinerator, inferiorresistivity of the film to cold weather and consequent inclination ofthe film toward rigidification, embrittlement and rupture.

As a result, increasing attention has come to be focussed on adoption ofpolypropylene (hereinafter referred to as "PP") type film for the shrinkwrapping method in recent years. Unfortunately, the PP film is inferiorin shrinkability to the PVC film. The drawn PP type film excels inmechanical properties, moistureproofness, heat seal strength, heatresistance, film modulus, and the like and, therefore, proves highlysuitable for use as a shrink wrapping film.

It is also advantageous over the PVC film in respect that the cost ofraw material and the specific gravity are both lower than those of thePVC film. Since PP is a rigid crystalline high polymer possessing a highsoftening point, the PP film shrink at higher temperatures than theconventional drawn films and exhibit a small shrink percentage at lowtemperatures in the neighborhood of 100° C. In the process of shrinkwrapping, therefore, the PP film must be heated at a higher temperature.Further because of sharp dependence of the shrink percentage upontemperature, the film in the course of wrapping undergoes locally unevenheating and entails uneven shrinkage which tends to induce suchphenomena as "wrinkles" and "unshrinking spots" which are highly quitedetestable from the viewpoint of practical use of the film. If the filmis amply heated to preclude these phenomena, there inevitably ensues theserious disadvantage that the article being wrapped is exposed toexcessive heating and the film itself loses transparency and sustainbreakage in the sealed portion or around air vents. The PP filmpreponderantly comes in thin thickness (ex. 15-25μ). If the thickness isincreased, the film gains in rigidity, tends to sustain breakage andconsequently proves no longer suitable for wrapping.

The conventional polyethylene type film, in its unmodified form, cannotbe given sufficient molecular orientation by drawing. The drawn film,therefore, exhibits low heat shrink percentage (particularly heat shrinkstress), high shrink temperature, inferior strength and opticalproperties, and insufficient binding force on wrapped articles. Thus,the film produced in a thickness fairly large by the standard ofordinary wrapping films is adopted for limited, special applications.

The ordinary polyethylene type film which has its molecules thoroughlycrosslinked by means of a high-energy ray and which has been amply drawnat a temperature exceeding the polymer's melting point enjoys highprocessibility, permits ready setting of molecular orientation bydrawing in a wide temperature range, exhibits high heat shrinkpercentage and heat shrink stress, and excels in comparison with theordinary polyethylene film in various properties such as opticalproperties including transparency and specular gloss, heat resistance,and the like. The film, however, shrinks at high temperatures andpermits no easy heat sealing. When the film is subjected to shrinkwrapping, therefore, it is degraded in strength, heat sealing property,and tear resistance and, consequently, is rendered susceptible to tear.

Further, the film suffers from problems such as great difficultyinvolved in the cutting and sealing of the film by use of an electricheat wire, degradation of physical properties, particularly opticalproperties, of the film in consequence of the heat shrinking treatment,degradation of film strength, infliction of rupture around the air ventsin the film during the shrink wrapping, and ready formation of wrinklesin the film. The film, accordingly, suffers from low packaging speed andinferior package finish.

As implied above, one critical property the film is required to possessfor successful shrink wrapping is the ability to permit satisfactorywrapping at low temperatures. This ability is particularly importantwhen the film is used for wrapping fresh foodstuffs.

The manufacture of a drawn film of PP is accomplished by a methodcomprising the steps of melt extruding the polymer resin through anextruder die, quenching the extruded tubular sheet, reheating the cooledtubular sheet at a high temperature within the range of from 150° to160° C., and forcing air into the inner cavity of the tubular sheet. Inthe case of a drawn film of low-density polyethylene, a similarlyextruded tubular sheet of the polymer resin is biaxially drawn in aneffort to set a high degree of molecular orientation in the film. In thecourse of the drawing, however, the sheet bursts, making the manufactureof film hardly practicable from the technical point of view.

Because of the difficulty, therefore, there is generally adopted adirect inflation method which comprises the steps of extruding thepolymer resin at a temperature within the range of from 180° to 220° C.,for example, and subsequently causing the extruded sheet, by means of aproper form of air, to be simultaneously cooled and inflated to aprescribed size.

This inflation method is characterized by being capable of producing thefilm inexpensively and very easily. The drawing effected in this method,however, causes disturbance and crystallization of the polymermolecules, degrades the film's optical properties, and fails to set themolecular orientation as desired. The film, therefore, has low heatshrink percentage and low heat shrink stress and shrinks at temperaturesrather high by any standard. Hence, the film produced in a largethickness barely finds utility in limited special applications. With aview to preventing the disturbance of molecules and permitting thedesired setting of thorough molecular orientation, there have beendeveloped different methods, including one comprising the steps ofmolding the low-density polyethylene, then exposing the molded polymerto a high-energy radiant ray under a suitable set of conditions forthereby causing partial crosslinking of the molecules and, thereafter,reheating the molded polymer and drawing it at the elevated temperature.The film obtained by the conventional method, nevertheless, is not freefrom the aforementioned disadvantages in any case.

Many methods have been proposed for producing a film by inflating amultilayered sheet incorporating layers of different polyolefins orlayers of both polyolefins and other polymers. For example, U.S. Pat.No. 3,682,767 discloses a film possessing improved melt strength andheat sealing property and exhibiting improved make-and-fill property inthe wrapping of a liquid article, manufactured by the steps of mixing acopolymer of ethylene and an olefinically unsaturated monomer such as,for example, ethylene-vinyl acetate copolymer (hereinafter referred toas "EVA") with a linear copolymer of ethylene of a density of 0.93 to0.96 g/cm³ and an α-olefin such as, for example, a modified high-densitypolyethylene (hereinafter referred to as "HDPE") and extruding theresultant mixture into a flat or tubular film. British Pat. No. 998,299teaches a printable polyethylene film which is produced by the steps ofmixing polyethylene such as low-density polyethylene (hereinafterreferred to as "LDPE") or HDPE with EVA, subjecting the resultantmixture to a crosslinking treatment, and drawing the mixture into afilm. And British Pat. No. 1,035,887 discloses a film excellent inlow-temperature strength and other properties, which is produced by thesteps of mixing LDPE with a linear medium-density polyethylene modifiedwith a small amount of butene and drawing the mixture.

As concerns methods proposed heretofore for the manufacture of films,British Pat. No. 998,299 mentioned above discloses a method whichcomprises causing crosslinking of molecules in the aforementionedcomposition by subjecting the composition to a treatment with a peroxideor high-energy radiant ray, heating the sheet to a temperature around orhigher than the melting point of polyethylene, and drawing the sheet asheld at that temperature and British Pat. No. 992,897 discloses a methodwhich comprises causing crosslinking of molecules in EVA by a treatmentwith a high-energy radiant ray, heating the sheet to an elevatedtemperature (preferably 100° to 120° C., for example), and drawing it atthat elevated temperature. The films obtained by using these methods orcompositions do not possess such outstanding optical properties,strength properties and low-temperature shrink properties as thoseobtained by the PVC film as described above, and they are also deficientin film-forming property and other similar properties.

Of the articles of the class which are packed by the shrink wrappingmethod, raw meat, processed meat, cheese, and other marine products andlivestock products generally have quite irregular shape and aresusceptible to deterioration due to the action of air. For protectionagainst the deterioration, therefore, such an article is shrink wrappedby first vacuum packaging the article with an O₂ -barrier film andshrinking the film with hot water for thereby causing the film tocontract and come into tight contact with the overall contour of thearticle. The package thus obtained prevents possible leakage of meatjuice or other liquid, preclude possible formation of wrinkles andoccurrence of pinholes particularly in the barrier layer of the film andbeautifies the outside appearance of the article contained. In the caseof the package described above, since the film is exposed to directcontact with the food article which generally has been stored at normalroom temperature or in a refrigerated space, the temperature of the filmis not readily elevated and the shrinking treatment performed at a hightemperature for a long time is detested as highly undesirable from thestandpoint of the preservation of freshness of the food under treatment.For the shrink wrapping of such articles, therefore, need is felt foradoption of a film which shrinks quickly at a very low temperature andexhibits high shrink tension and heat sealing property. From thestandpoint of workability, the film is required to possess modulus andcold resistance. A typical example of the conventional films whichsatisfy this requirement is offered by U.S. Pat. No. 3,741,253, whichteaches a method comprising the steps of first preparing an innermostEVA layer in a tubular form, causing crosslinking of molecules in thislayer with a treatment using a high-energy radiant ray, then coatingthis tubular layer with an O₂ -barrier layer of vinylidene chloridepolymer, subsequently fusion superposing another EVA layer on the coatedtubular layer, and thereafter drawing the multilayered sheet at atemperature such as 88° C. which causes no appreciable high molecularorientation of the vinylidene chloride type polymer and under conditionswhich cause no appreciable high molecular orientation of the otherpolymers used in the film in comparison with this invention. This filmincorporated an O₂ -barrier layer made of a vinylidene chloride typepolymer. In this case, the method used for the manufacture of the filmis so complicate as to render the quality control both difficult andexpensive, the component layers of the film suffer from complicatethermal hysteresis and consequently are deprived of the effect of suddencooling, and the drawing stability of the sheet is governed by theparticular component EVA. If the drawing is carried out at a temperaturefalling short of 88° C., for example, the sheet being drawing sustainspuncture so readily as to render the drawing impracticable.Consequently, the shrink property of the film is degraded, the degreesof orientation of the component layers even including the vinylidenechloride type layer are lowered, and various other properties arelikewise impaired. Besides, because of the crosslinking in the innermostlayer, the film exhibits poor heat sealing property and becomessusceptible to curling. In addition, the film suffers from thephenomenon of layer separation in the course of the shrinking treatment.The vinylidene chloride layer, generally when it is quenched in thepreparation of the raw sheet, assumes an amorphous rubbery state andthen, with lapse of time, undergoes gradual crystallization. Thiscrystallization tends to start within several minutes of the formationof the amorphous rubbery layer at the normal temperature. If, at thistime, the layer is exposed to heat as from the lamination, it maypossibly be deprived of the effect of quenching or the uniformity oftexture. When the quenched layer is left to undergo crystallization inthat case, it no longer exhibits elasticity and becomes brittle. Thisembrittlement tends to occur also when the drawing is effected at a veryhigh temperature. Even when this layer is used as an inner layer in thefilm, a bend given to the film results in the formation of pinholes inthis inner layer and the film, therefore, no longer retains its barrierproperty. Generally, for the vinylidene chloride type polymer tomanifest its strength and other properties to advantage, it is extrudedthrough a die directly into cold water (cooled to 8° C. with ice, forexample) to assume an amorphous rubbery texture. It cannot produce afilm of well-balanced strength properties unless it is drawn at anextremely low temperature (such as 30° C., for example). Under theseconditions, the crystallization is generally accelerated by theorientation due to the drawing so that the crystallization issubstantially completed in the course of the drawing and the molecularorientation is stably set by the end of the crystallization. When thedrawing is carried out at a higher temperature, the molecularorientation in the vinylidene chloride layer begins to proceed graduallyafter the drawing of the other component layers of the film have beenbrought to completion. The film which is consequently obtained possessesa substantially low degree of molecular orientation and lacks strength,resistance to infliction of pinholes, and shrinking property. In thiscase, there is a wide gap between the temperature range in which the EVAresin (such as near melting point, for example) can be drawn and theoptimum temperature range in which the vinylidene chloride resin (suchas 30°-35° C., for example) can be drawn. After all, the temperature atwhich the film can be stably drawn falls around the aforementionedtemperature range even when the temperature for effective drawing of theinnermost layer is lowered, though to a slight extent, by means ofcrosslinkage and the proportion of the thickness of the innermost layerto the combined thickness of the remaining component layers of the filmis substantially increased, say to 75%. The temperature may be decreasedif the vinyl acetate content of the EVA polymer which is the principlelayer was increased. The increased vinyl acetate content of the EVApolymer, however, brings about a serious disadvantage that the film isheavily degraded in shrinking property, shrink tension, heat-sealingproperty, heat resistance, strength, elastic modulus and the like andfurther impaired in time-course stability.

SUMMARY OF THE INVENTION

The inventors continued a study with a view to mending the variousdisadvantages suffered by the conventional films and methods touchedupon above. This study has led to development of a cold drawnhigh-orientation multilayered film and a process for the manufacture ofthe film which, owing to synergistic combination of the cold drawabilityof a specific resin and the high cold orientation effected in principalcomponent layers of film, enjoys improvements in its strengthproperties, particularly impact strength, heat-sealing property, opticalproperties, surface property and other special functions without anyimpairment of other properties. This film combines a special function ofthe characteristics which the conventional polyolefin type films,plasticized PVC type film, and PP type film and those of themultilayered film cannot posess. The process by which this excellentfilm of the present invention is manufactured relies on the synergism ofthe specific composition of raw materials and the stratal constructionof component layers of film and, therefore, excels in the performance ofthe work of film drawing.

An object of this invention is characterized by providing a shrinkingfilm which exhibits outstanding heat shrink properties, i.e. heat shrinkpercentage and heat shrink tension particularly at low temperatures, andgenerous dependence of the heat shrink property upon temperature. Itshould be noted, however, that the present invention is not limited tothe film's excellence in this respect alone.

The film of this invention is a cold drawn high-orientation multilayeredfilm, having a tensile strength of not less than 5.0 kg/mm², theprincipal component layers of said film being highly oriented andincluding at least one layer preponderantly containing a cold-drawableresin selected from the group consisting of blended and unblendedspecific polymers, [1] (B)+(A)+(C), [2] (B)+(A), [3] (B)+(C), [4] (D),and [5] (E), wherein,

(A) is at least one ethylene type polymer selected from the groupconsisting of copolymers of ethylene with other monomers such as vinylesters, aliphatic unsaturated carboxylic acids and alkyl esters of saidcarboxylic acids, ionically crosslinked resins derived from saidcopolymers, and low-density polymers of ethylene,

(B) is a soft copolymer elastomer having a Vicat softening point of notmore than 60° C.,

(C) is at least one polymer selected from the group consisting ofcrystalline polypropylene, high-density polyethylene, crystallinepolybutene-1 and polymethyl pentene-1,

(D) is a crystalline polybutene-1 having a concentration of 50 to 100%by weight, and

(E) is an ionically crosslinked resin.

And, another object of the present invention is to provide a process forthe manufacture of the multilayered film, which comprises extruding acold drawable resin into a molten sheet or film, quenching it tosolidify, preparing a multilayered raw sheet or film including the colddrawable resin layer at least one, cold drawing the multilayered rawsheet or film at a temperature within the range of from 20° to 80° C. toan area stretching ratio in the range of from 3 to 30 times the originaldimension and thereby allowing all the component layers of the sheet orfilm to be stretched to a high degree and causing the principalcomponent layers of the sheet or film to be oriented to a high degree.The film produced as described above is characterized by manifestingsuch a high degree of orientation by stretching as has never beenattained to date as well as other outstanding properties owing to thesynergistic combination of the composition of specific polymers and thestratal construction of component layers and other layers of differentresins.

The film which has high degree of orientation uniformly imparted to eachof the component layers of film and which excels particularly instrength, transparency, and other various properties can be obtainedquite stably under conditions such as low-temperature conditions whichdepart from the individual drawing conditions proper to the respectivespecific polymers and other resins making up the multilayered raw sheetor film, viz. the conditions under which the respective specificpolymers and other resins can never be drawn effectively. The film ofthis invention possesses properties appropriate for the film to beadvantageously applied to various forms of wrapping, especially but notlimitatively to shrink wrapping. The film can be made to excelparticularly in optical properties, strength, heat-sealing property,gas-barrier property, low-temperature shrink property, and shrinkresponse (speed).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the interrelationship between the shrinkpercentage of the film and the heat-treating temperature.

FIG. 2 is a graph showing the interrelationship between the shrinktension of the film and the heat-treating temperature.

In FIGS. 1 and 2, the curve 1 shows the film of the present inventionRun No. 1, the curve 2 shows the film of the present invention Run No.7, the curve 3 shows the film of the present invention Run No. 12, thecurve 4 shows the plasticized PVC shrink film 17μ in thickness of thecomparative sample (a), the curve 5 shows the PP shrink film 16μ inthickness of the comparative sample (b), the curve 6 shows thecommercial uncrosslinked and LDPE shrink film 50μ in thickness, thecurve 7 shows the crosslinked polyethylene shrink film 17μ in thickness,the curve 8 shows the barrierable shrink film 71μ in thickness, and thecurve 9 shows the barrierable shrink film 69μ in thickness.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of improving the various properties of crystallinepolypropylene (hereinafter referred to as "IPP"), particularly thethermal resistance, low-temperature strength and impact strength,Japanese Patent Publication No. 7088/1960, Japanese Patent PublicationNo. 15042/1961, Japanese Laid-open Patent Publication No. 78977/1977,etc. have disclosed methods for formulating compositions using IPP asthe main component and additionally incorporating ethylene-propylenecopolymer rubber (hereinafter referred to as "EPR") as a minorcomponent. In the compositions obtained by these methods, however, sincethe compatibility of IPP and EPR is not necessarily high, thecompositions molded in the form of a thin film have coarse surface,exhibit very poor optical properties and offer insufficient strength.With a view to mending this disadvantage, if to only a slight extent,methods for formulating compositions which further incorporate amorphousatactic polypropylene as an additional component have been proposed byJapanese Laid-open Patent Publication No. 112946/1974, JapaneseLaid-open Pat. Publication No. 96638/1973, etc. U.S. Pat. No. 3,832,270discloses a method which comprises coating a layer of crosslinkedpolyethylene with a layer of a composition using IPP as the maincomponent and incorporating the mixture of an atactic PP andpolybutene-1 (hereinafter referred to as "PB-1") as a minor componentand drawing the composite sheet at 100° C. This method is claimed toimprove the tear strength of the produced film. All these methodsinvariably contemplate effecting desired improvements by incorporationof additives preponderantly comprising PP. The compositions obtainedaccording to these methods, when molded in the form of a thin film,still suffer from difficulties relating to dispersibility of additivecomponents in the main component, film strength, thermal resistance,sealing property and the like.

The composition of the blended specific polymers [1], [2] and [3] whichis used in the present invention is capable of not only improvingsynergistically the heat seal property, various strength properties,flexibility, transparency, moderate stiffness of film (fair modulus ofelasticity), resistance to heat, resistance to cold, and adhesivenesswith layers of other resins and permitting free adjustment of filmtexture in a wide range from fair softeness to high rigidity. It is alsocapable of enabling layers of other resins which, when used alone, cannever be drawn under the conditions contemplated by the presentinvention to be successfully drawn when handled in conjunction with thespecific component layers of the film of this invention, manifests aneffect of conspicuously improving the workability of such resin layerson a synergistic scale and imparting fully balanced properties to theproduced film.

In another embodiment of this invention, the multilayered film isproduced by preparing a multilayered raw sheet or film including a layercontaining the polymer (D) of the specific polymer [4] (e.g.,crystalline polybutene-1) and cold drawing the sheet under the specificconditions described herein below. This film is characterized bymanifesting a heretofore unattainable high degree of orientation andother excellent properties owing to the synergism of the attributes ofthe aforementioned polybutene and those of the layers of other resins.

Under conditions such as, for example, low-temperature conditions whichdepart from the individual conditions proper to the aforementionedpolybutene-1 and the other specific polymers making up the multilayeredraw sheet or film, viz. the conditions under which the respectivespecific polymers and other resins can never be effectively drawn, therecan be produced the film which has high degree of orientation uniformlyimparted to each of the component layers of film and which excelsparticularly in strength, transparency, and other various properties.This film manifests characteristics which are totally different fromthose exhibited by a film produced solely of a layer of polybutene-1.When the sheet formed solely of a layer of polybutene-1 is drawn, theproduced film is flushed and consequently shows poor optical properties.This film is deficient in tensile strength, tear strength, heat shrinkpercentage and heat shrink tension, and in seal properties as well.Totally unlike this film, the film of the present invention possessesproperties appropriate for the purpose of various forms of wrapping,particularly but not limitatively of shrink wrapping.

Specifically, this film is excellent in tensile strength, impactstrength, sealing strength, optical properties, and shrink property.

In yet another embodiment of this invention, there is obtained a film ofexcellent properties by preparing a multilayered sheet including onelayer formed of the polymer (E) of the specific polymer [5] which is anionically crosslinked resin and cold drawing the sheet under specificconditions.

The polymer (A) of the blended specific polymers [1] and [2] is apolymer of relatively low crystallinity (falling within the range offrom 60 to 10% as determined by the X-ray method) with consistencyintermediate between the degrees of rigidity and softness. It isselected from the group consisting of copolymers of ethylene with vinylester monomer, aliphatic unsaturated carboxylic acids and alkyl esterderivatives of said carboxylic acids and LDPE. Desirable examples of thespecific polymer (A) are EVA, ethylene-ethyl acrylate copolymer (EEA),ethylenemethyl methacrylate copolymer (EMMA), ethylene-acrylic acidcopolymer (EAA), ethylene-methacrylic acid copolymer (EMA), an ionicallycrosslinked resin which is a copolymer of ethylene and aliphaticunsaturated carboxylic acid, the carboxyl group of said copolymer beingat least partially ionized with metal, and said ionically crosslinkedresin is obtained by at least partially saponifying an aliphaticunsaturated alkyl carboxylate and then subjecting the product ofsaponification to at least partial ionic bonding with metal. Thecombined amount of the component monomers of such a copolymer exceptingethylene is desired to fall within the range of from 1 to 13 mol%,preferably from 2 to 12 mol%. When this amount exceeds 1 mol%, theproduced film excels in seal property, flexibility, various strengthproperties, and the like. When the amount exceeds 13 mol%, however, thefilm is deficient in extrudability, compatibility with other components,drawability, and the like. When this specific polymer is extruded in theform of a film, particularly in the outer layer, it exhibits inferioroptical properties, low strength and poor resistance to heat, with theresult that the opposed surfaces of adjacent layers in the film tend toinduce the phenomenon of mutual blocking even to the extent of renderingthe film handling difficult. The melt index [determined in accordancewith ASTM D-1238 (190° C.)] of the specific polymer generally fallswithin the range of from 0.2 to 10, preferably from 0.3 to 5. When themelt index (MI) falls below 0.2, the compatibility of the components ofthe composition and the extrudability of the resulting blend of suchcomponents are not satisfactory. When MI exceeds 10, the blend as thebasic material at times fails to provide sufficient strength. While thesheet is being drawn, for example, the bubble formed in the process ofinflation tends to sustain rupture. These adverse inclinations aresimilarly experienced when the sheet is given a post-treatment forcrosslinking. Of the various copolymers usable as the polymer (A) in thecomposition of the present invention, EVA proves to be the mostdesirable polymer. In the case of LDPE, there are times when it provesdesirable to increase the amount of the polymer (B) or subject thepolymer to a treatment for crosslinking.

The soft copolymer elastomer as the polymer (B) of the blended specificpolymers [1], [2] and [3] is selected from the group consisting ofelastomers possessing a Vicat softening point (hereinafter referred toas "VSP") of not more than 60° C., or preferably not more than 50° C.,more preferably not more than 40° C., such as, for example, copolymerelastomer of ethylene with an α-olefin, buthyl rubber andblock-copolymerized thermoplastic elastomers of styrene-conjugateddiene. Of these possible elastomers, the ethylene-α, -olefin copolymeris more preferable. This is a soft copolymer which is formed of ethylenewith at least one α-olefin selected from the group of α-olefins havingfrom 3 to 12 carbon atoms. Optionally, these two monomers may further becopolymerized with a small amount of a hydrocarbon possessing thestructure of polyene such as, for example, dicyclopentadinene,1,4-hexadiene or ethylidenenorbornene. Concrete examples of α-olefinsusable for this purpose include propylene, butene-1, hexene-1,heptene-1, 4-methyl-1-pentene, and octene-1. Of these α-olefins,particularly desirable are propylene and butene-1. The ethylene contentof the copolymer is desired to fall within the range of from 20 to 90mol%, preferably from 40 to 90 mol%, and more preferably from 65 to 89mol%. The most preferable range of the ethylene content is from 70 to 88mol%.

The ethylene-α-olefin copolymer is of nature such that the density doesnot exceed 0.91 g/cm³. VSP (value determined by the method of ASTMD-1525 under 1 kg of load) of the polymer (B) is not more than 60° C.preferably 50° C., more preferably 40° C. Generally, the crystallinityof the polymer in the rubbery zone ranges from substantial amorphousnessto low partial crystallinity of the order of not more than 30% asdetermined by the X-ray method. The ethylene-α-olefin copolymerelastomer is particularly desired to be a copolymer of ethylene withpropylene or butene-1. This copolymer, optionally, may contain a smallamount of a compound possessing the structure of diene as anothercopolymerizable monomer. For example, this compound is a thermoplasticelastomer possessing MI within the range of from 0.1 to 10, preferablyfrom 0.2 to 6, which elastomer is a random copolymer produced by apolymerization using a catalyst composed of a vanadium compound and anorganic aluminum compound. This elastomer is desired to lack the blockedform which is generally possessed by ordinary unvulcanized rubber,refrain from inducing the phenomenon of cold flow, come in the form ofpellets, and possess ample thermoplasticity enough to be extruded all byitself into film. A typical proprietary product that meets thisrequirement is "Tafmer" produced by Mitsui Petrochemical Industries,Ltd.

The polymer (C) of the blended specific polymers [1] and [3] is at leastone member selected from the group consisting of IPP, HDPE, and highpolymerized crystalline PB-1. This polymer (C) has relatively highrigidity and desirably VSP of not less than 100° C. IPP is the kind ofIPP with high isotacticity usually available on the market. It isdesired to be a homopolymer of propylene or a copolymer of propylenewith not more than 7 mol% of ethylene, 1-butene or some other α-olefin.It may be a mixture of these co-monomers.

HDPE is the kind of polyethylene which is produced by the medium- orlow-pressure process and possesses a density of not less than 0.935(g/cm³) and is usually available on the market. It is desired to possessMI within the range of from 0.1 to 10, preferably from 0.2 to 7. It mayembrace a copolymer of ethylene, in which case the ethylene content isdesired to exceed 93 mol%, preferably 95 mol%. When MI is less than 0.1,this polymer tends to pose problems relating to compatibility andoptical properties in the course of molding. When MI exceeds 10, thepolymer as the basic material does not offer sufficient strength andexhibits inferior film-forming property. Of the group of members fromwhich the polymer (C) is selected, it is preferable to usepreponderantly IPP. A mixture of polypropylene with HDPE may beadvantageously used instead. A rigid polymer which possesses properdegrees of compatibility and dispersibility and, therefore, fulfils thepurpose of this invention may be used. When HDPE is used as the polymer(C), it is preferable to crosslink before it is drawn.

The polymer (D) of the specific polymer [4] is crystalline PB-1 which isa highly isotactic, ultra-high molecular polymer obtained bypolymerizing butene-1 as a principal monomer. It may embrace a copolymerobtained by copolymerizing butene-1 with other olefinic monomer in sucha way that the principal monomer, butene-1, is allowed to retain itscrystallinity intact. In this copolymer, the content of butene-1 isdesired to exceed 85 mol%, preferably 90 mol% and MI is desired to fallwithin the range of from 0.2 to 20, preferably from 0.2 to 6. The PB-1of this type are different from polybutenes of the type which areprepared as polymers of poly-iso-butylene and are used as liquid or waxyadditives of low degrees of polymerization. When PB-1 is used as thepolymer (C), the PB-1 content in the blend of polymers forming the layerof cold drawable resin is desired not to exceed 50% by weight.

The polymer (E) of the specific polymer [5] is an ionically crosslinkedresin which is a copolymer of ethylene and aliphatic unsaturatedcarboxylic acid, the carboxyl group of said copolymer being at leastpartially (including wholly) ionized with metal, and said ionicallycrosslinked resin is obtained by at least partially (including wholly)saponifying an aliphatic unsaturated alkyl carboxylate and thensubjecting the product of saponification to at least partial ionicbonding with metal. Said metal is such as, for example, Na⁺, Zn⁺⁺,Mg⁺⁺ - - - . There are cases when the specific polymer is desired toretain therein the ester bond, depending on the purpose for which thepolymer is used.

The layer of cold drawable resin in the film of the present invention issubstantially composed of specific polymers described above. Thesespecific polymers [1], [2], [3], [4] and [5] may be used as mixed withother suitable polymers within the limits in which they are allowed toretain their characteristics unaffected. The content of the specificpolymers in the cold drawable resin layer ought to exceed 50% by weightat all times.

Among the polymers (A), (B) and (C), therefore, the allowablecombinations are [1] (B)+(A)+(C), [2] (B)+(A) and [3] (B)+(C) and thepreferable mixing ratios by weight of component polymers in thecombinations are such as:

0.90≧B/(A+B)≧0.05 and 2.0≧C/(A+B)≧0.05 in [1]

0.90≧B/(A+B)≧0.05 in [2]

0.90≧B/(B+C)≧0.30 in [3]

and more preferably:

0.70≧B/(A+B)≧0.07 and 1.0≧C/(A+B)≧0.10 [1]

0.70≧B/(A+B)≧0.07 [2]

0.87≧B/(B+C)≧0.40 [3]

and more preferably:

0.50≧B/(A+B)≧0.08 and 1.0≧C/(A+B)≧0.10 [1]

0.50≧B/(A+B)≧0.08 [2]

If the amount of the soft polymer (B) is less than the allowable lowerlimit indicated above, the blend of any of the [1], [2] and [3]combinations does not easily manifest the expected synergistic effect ofcold drawing property and, therefore, suffers from inferior properties.For example, the blend may be deficient in film strength, opticalproperties, low-temperature properties, softness, sealing property,drawability, and the like. If the amount is greater than the allowableupper limit indicated above, the produced film tends to acquireexcessive flexibility, cause blocking and lose thermal resistance,sealing property and optical properties.

Among the combinations of the specific polymers indicated above,particularly desirable is the combination [1] (A)+(B)+(C). To be morespecific, the polymer (C) cooperates with other components to improvesynergistically the film's tensile and impact strengths, heatresistance, extrusion moldability, modulus of elasticity and heatsealing property. The improvement is especially conspicuous in heatresistance, extrusion moldability, modulus of elasticity and heatsealing property. When the content of the polymer (C) is less than theallowable lower limit, the blend suffers from considerable deficiency infilm workability, unevenness of film wall thickness due to inferiorflowability of the blend in the die. Further, the improvement ascriableto the polymer (C) is degraded in heat sealing property and strengthproperties. The heat resistance also falls short of the expected level.If the content of the polymer (C) in the blend is greater than theallowable upper limit indicated above, the blend is deficient inextrusion moldability, transparency, flexibility and impact strength.Thus, this content ought to fall within the range indicated above. Amongthe aforementioned group of polymers from which the polymer (A) isselected, particularly desirable is a specific ethylene type copolymer.There are cases wherein this particular copolymer is desired to form theprincipal component in the ternary blend of the aforementionedcombination of (A)+(B)+(C).

In the absence of the polymer (B) from the aforementioned ternary blendof the combination (A)+(B)+(C), both the blendability and combatibilityare not very satisfactory and the synergistic effect mentioned abovecannot be expected. In the present of the polymer (B), the ternary blendno longer suffers from such deficiency.

One possible reason may be that the ethylene contained in the polymer(A), the characteristics of the polar functional group issuing from thepeculiar structure thereof, and the other polymers (B) and (C)delicately interact and, at the same time, the crystalline structure ofthe blend, the condition of the dispersion of the component polymers inthe blend, the effects of the treatment and other factorssynergistically cooperate with one another.

In the case of the blend of the aforementioned combination wherein thepolymer (A) forms the principal component, when the three componentpolymers each in the form of pellets are blended dry, then melted,kneaded and extruded into a film by use of an extruder excelling inblending capacity, a possible result of the extrusion molding is suchthat either inside or around the particles of the polymer (C) dispersedwithin the polymer (A), the polymer (B) is dispersed in a complicatepattern and allowed to react upon and interact with the polymer (C).

The condition in which such component polymers are dispersed when theblend is molded into a film and drawn for necessary orientation varieswith the condition for the molding of the blend.

When the aforementioned blend is extruded at a relatively hightemperature within the range of from 230° to 260° C. through a film orsheet die containing a narrow slit 1.5 mm in thickness, either under noload or under a fixed drawing ratio, and is quenched to produce a film,for example, the properties of the resulting film depend on the kind andamount of the rigid polymer (C) used in the blend. When the polymer (C)happens to contain 30% by weight of PP, for example, some portion of thePP in the polymer (C) is distributed in the principal polymer (A) to theflowing direction and the dispersed particles of PP are arranged in theform of fibers, with the result that the film acquires a structure asthough reinforced with glass fibers and, therefore, manifests variousstrength properties at highly improved level. When the raw sheet or filmis crosslinked before drawing, the characteristic structure resemblingthat which is reinforced with glass fibers may at times be manifested toadvantage. The additional crosslinking, therefore, is no essentialrequirement.

In the blend of the combination (B)+(C), the thermoplastic elastomerwhich is particularly advantageously used as the polymer (B) is a randomcopolymer composed of 65 to 95 mol%, preferably 75 to 90 mol%, ofethylene, amorphous or partially low crystalline propylene and butene-1.This elastomer is available in the form of pellets.

The specific combination of polymers or the polymer (E) to be used inthe specific multilayered film of the present invention is extruded inconjunction with other resins into a multilayered sheet. Then, the sheetmay be activated with a high-energy ray such as electron beam (β ray), γray or U.V. ray so as to be modified through a crosslinking reaction.This post-treatment is desired to be effected to an effect such that thecontent of gel insoluble in boiling xylene falls within the range offrom 0 to 50% by weight, MI does not exceed 0.5. Preferably, the contentof gel is in the range of from 0.1 to 40% by weight and MI is below 0.1.

If the insoluble gel content is greater than the allowable upper limitindicated above, the product of molding suffers from degradation ofelongation and strength. When this product is in the form of a film, theheat sealing property is degraded to a point where the film cannoteasily be sealed or cut with a hot wire or it tends to tear. Thus, theinsoluble gel content is desired to fall within the range indicatedabove.

The polymer (D) is a polymer composed preponderantly of crystalline PB-1and is identical to the polymer touched upon previously in thedescription of the polymer (C). In the layer formed preponderantly ofthis PB-1, the polymer (D) is desired to be contained by not less than50% by weight, preferably by not less than 70% by weight, and morepreferably by not less than 80% up to 100% by weight.

The polymer (E), too, is desired to be contained by not less than 50% byweight.

The film of the present invention is characterized by containing atleast one layer formed of specific polymers selected from the blendedand unblended specific polymers [1], [2], [3], [4], and [5]. By virtueof the high cold drawability (synergistically manifested particularlywhen the specific polymers are used in a plurality of layers) possessedby these specific polymers, other layers formed of resins which defycold drawing can be simultaneously drawn to a high extent. It issurprising to note that, in the film of this invention, IPP can be drawnat 32° C. as well be described afterward. The specific polymers of thepresent invention permit orientation to be effected to degrees normallyunattainable and, therefore, give birth to the aforementionedcharacteristics of the present invention. It goes without saying thatthe multiple layers of the film of this invention can be formed solelyof the specific cold drawable resins instead of being interposed bylayers of other resins.

The specific polymers described above are resins which permit colddrawing and high orientation. The elastomer as the polymer (B) iscontained where the polymer (D) or (E) is contained by less than 50% byweight or not contained at all. The specific combinations of polymers[1] (B)+(A)+(C), [2] (B)+(A) and [3] (B)+(C) go to manifest highcapacities for cold drawing and high orientation. Of the specificpolymers involved in this invention, the specific polymer of [4] (D)possesses the highest cold drawability, followed by the specificpolymers [1], [2], [3], and [5]. Especially for the specific polymer [4](D) to manifest its outstanding effect to advantage, the content of thispolymer in the layer is desired to exceed 50% by weight as describedabove.

The resins for the other layers which may be incorporated in the film ofthis invention in addition to those of the specific cold drawable resinsare generally selected from the group consisting of IPP, polyethylene(PE), EVA, copolymers of ethylene with aliphatic unsaturated carboxylicacids or carboxylates, and ionically crosslinked resins (Io) derivedfrom ethylene type copolymers.

The resins usable for the O₂ -barrier layer which may be incorporated inaddition to the layers of the specific cold drawable resins aregenerally selected from the group consisting of compositions formedpreponderantly of vinylidene chloride type copolymer (PDC), saponifiedpolymers of ethylene-vinyl acetate copolymer, nylon type resin (Ny), andpolyester type resin (PET). Where the produced film is required topossess particularly high shrink property, it is desirable to use thePDC type polymer.

Though the above specified polymers mostly function as an adhesivelayer, the adhesive layer may be used additionally for adhering layers.Examples of the layers used as the adhesive layer are selected from thegroup consisting of EVA containing comparatively high vinyl acetatecontent (VAC 15-40% by weight), ethylene-α-olefine copolymer elastomers,ethylene-aliphatic unsaturated carboxylic acid copolymers and modifiedderivatives thereof, stereo block-copolymer of styrene-conjugated dienetype monomers and thermoplastic polyurethane type polymers. The producedfilm is sometimes sufficient by including at least one layer possessingat least one polymer selected from the above group depending on itspurpose.

As regards the thickness distribution of the component layers in thefilm, although the proportion of the combined thickness of the layersformed of the specific polymers [1], [2], [3], [4], and [5] to the totalthickness of all the layers of the film is not specifically limited, itis nevertheless desired to exceed 20%, preferably 30%, more preferably50% and most preferably 60%. It may be suitably fixed to suit thepurpose for which the produced film is used in the particualr case.Concerning the combination of component layers in the film, it isproposed for the sake of simplicity to refer to the combined specificpolymers [1] (B)+(A)+(C), [2] (B)+(A) and [3] (B)+(C) collectively asSBC, to the specific polymer [4] (D) as PB, and to the specific polymer[5] (E) as Io respectively.

Examples for the two-layered films, typical combinations of componentlayers are as follows:

(a) SBC/PP, SBC/Ny, SBC/EVA, SBC/Io, - - -

(b) PB/PP, PB/Ny, PB/EVA, PB/Io, - - -

For the three-layered and other multi-layered films, typicalcombinations of component layers are as follows:

(a) PP/SBC/PP, Ny/SBC/Ny, PP/SBC/Io, Io/SBC/Io, EVA/SBC/EVA,PP/SBC/EVA, - - -

(b) PP/PB/PP, Ny/PB/Ny, PP/PB/Io, EVA/PB/EVA, PP/PB/EVA, - - -

It is optional to add to these combinations the aforementioned layer ofadhesive resin. These combinations are effective in improving surfacehardness and sealing property, in improving modulus of film andmechanical properties for the sake of packaging, and in improvingmechanical strength properties and transparency. In the case of a layerto be formed of other resin which is highly functional and costly, thethickness of the layer may be substantially decreased to the order of0.1 to 10μ. It is strinking to note that, in the film of the presentinvention, the layer of such a thin thickness can be effectively colddrawn. The proportion of the thickness of this layer is desired to fallwithin the range of from 0.1 to 30%, preferably from 0.1 to 20%, andmore preferably from 0.1 to 10%. Even when the intermediate layer (SBC)in the three-layered film mentioned above is replaced by a layer ofother resin and the aforementioned extremely thin layer of the highlyfunctional and costly resin is incorporated, the resultant film proveshighly advantageous because the component layers are allowed to manifestfully their characteristic properties such as sealing property andthermal resistance. For example, in the manufacture of a film possessingproperties befitting the general shrink wrapping, particularly highstrength and low-temperature high-speed shrinking property, by adoptionof a highly effective combination of SBC or PB layers, incorporation ofthe layers of propylene type resin and PVC type resin (including aplasticizer) generally available in the market permits the produced filmto enjoy the advantages derived from the two resins mentioned above.Thus, there can be obtained a film which exhibits the advantageousproperties of an ordinary PP type film such as surface slipperiness,adaptability to the wrapping machine, high shrink ratio, high shrinktension, great ease of fusion cutting with a hot wire or hot blade,sealing property, and high heat seal strength and, on the other hand,shuns the disadvantages of the PP type film such as gradual loosing offilm in packages with lapse of time, rupture due to excessive tension,deficient impact strength, poor tear strength, insufficient coldresistance, defective shrink wrapping property at elevated temperatures,inclination toward sudden shrinkage due to change of temperature, andlimited adaptability for shrink wrapping and the like, or a film whichpossesses an outstanding capacity for elastic recovery and also exhibitsthe advantageous properties of a PVC type film such as low-temperatureshrink wrapping property, flat temperature characteristics for shrinkageand favorable optical properties and, on the other hand, shuns thedisadvantageous properties such as poor heat seal property (especially,said fusion sealing property), gradual degradation of properties ingeneral with lapse of time and occurrence of noxious gases during thecutting and sealing of film and in the course of incineration of filmwaste. To cite a concrete example, there can be produced a cold drawnhigh-orientation three-layered film (15μ) of the combination of PP/PB/PPwherein the first (PP) layer has a thickness of 1.5μ, the second (PB)layer a thickness of 12μ and the third (PP) layer a thickness of 1.5μ.This film may incorporate therein an adhesive layer such as EVA,ethylene-α-olefin copolymer or the like. In the case of thiscombination, incredulously a film of fair strength having an extremelysmall total thickness of 6μ to 7μ can be obtained as shown in a workingexample cited herein below. Another cold drawn high-orientation filmwhich can be produced has a total film thickness of 15μ, consisting ofthe first (PP) layer of a thickness of 0.5μ, the second (SBC) layer of athickness of 14μ and the third (PP) thickness of 0.5μ. Again this filmmay incorporate therein an adhesive layer such as of EVA,ethylene-α-olefin copolymer or the like.

When one layer of the aforementioned crystalline PB-1 (PB) isincorporated as an inner layer and at least one adhesive layer isfurther incorporated in the aforementioned films, such additional layersserve the purpose of giving stabilized drawability into the films and,at the same time, improving various properties of the films. Toillustrate the synergistic effects brought about by the incorporation ofsuch layers by citing data from the working examples given afterward,while the film cold drawn solely of SBC in Run No. 1 of ComparativeExample showed 1.4% of Haze, 11.55 Kg/mm² of tensile strength, 220% ofelongation, 33 Kg/mm² of modulus of elasticity, 1.1 Kg/15 mm width ofheat seal strength (sealing method by fusion cutting), 60° C. astemperature for 20% shrinkage, 24 Kg.cm of dart impact strength, thethree-layer film of a construction consisting of 0.5μ of PP layer, 15μof SBC layer and 0.5μ of PP layer and produced in Run No. 20 of Exampleof this invention showed 0.8% of Haze, 14.1 Kg/mm² of tensile strength,170% of elongation, 40 Kg/mm² of modulus of elasticity, 2.1 Kg/15 mmwidth of heat seal strength, 58° C. as temperature for 20% shrinkage and32 Kg.cm of dart impact strength, indicating notable improvement in thevarious properties indicated. The improvement in modulus of elasticityand heat seal strength was particularly conspicuous despite the factthat the cold drawn PP layers each had a very thin thickness. It is alsonoteworthy that the film of this invention retained its low-temperatureshrink property amply despite the fact that the PP layers wereincorporated on the outer sides of the film. To be more specific aboutPB-1, the PB layer is allowed to manifest its special synergistic effectto advantage only when it is incorporated in the multi-layered filmcontemplated by this invention. When the PB-1 resin is drawn all byitself, the produced film suffers from totally inferior properties. Whenit is drawn in the multi-layered film, however, the cold drawingstrength which this particular layer exhibits is greater than thatexhibited by the SBC layer in most cases. More desirable results areobtained when the PB layer is incorporated as an inner layer.

To be more concrete, the outstanding synergistic effects brought aboutby having the PB-1 layer interposed as an inner layer in the film isevident from the following comparison: The film obtained by using PB-1alone as in Run No. 3 of Comparative Example showed very poor physicalconstants such as 25% of Haze, 4.2 Kg/mm² of tensile strength, 30% ofelongation (a value suggesting high susceptibility to tear), 0.35 Kg/15mm width of heat seal strength, 83° C. as temperature for 20% shrinkage(a value suggesting lack of heat shrink property at low temperatures),45 g/mm² of shrink tension, and 11 Kg/mm² of modulus of tensile, whereasthe aforementioned three-layered film produced in Run No. 9 of Exampleof this invention showed highly desirable physical constants such as0.6% of Haze, 16.5 Kg/mm² of tensile strength, 210% of elongation 2.8Kg/15 mm width of heat seal strength, 62° C. as temperature for 20%shrinkage (a value suggesting high heat shrink property at lowtemperatures), 350 g/mm² of shrink tension, and 52 Kg/mm² of modulus oftension. Despite the absence of an adhesive layer between the layers ofPP and PB, an attempt to separate the two layers from each other bymeans of a cellophase tape ends up in failure for some unknown reason.This means that these two layers have sufficient adhesive strength. Thesealing effect which they produce is much higher than when the twolayers are used independently of each other. In the field shrinkwrapping test, it is demonstrated that the aforementioned film of thisinvention possesses as high shrink properties at low temperatures as thePVC type film and also possesses the elasticity normally required of anyfilm used satisfactory for the purpose of wrapping. Thus, this filmproves quite suitable for wrapping film.

The aforementioned film of the construction consisting of the threelayers of Io/SBC/Io constitutes itself an excellent shrinking film. Thefilm as produced in Run No. 3 of Example of this invention shows highlyadvantageous physical constants such as 0.6% of Haze, 11.5 Kg/mm² oftensile strength, 245% of elongation, and 2.2 Kg/15 mm width of heatseal strength and also exhibits high shrinkability at low temperaturesand high modulus of elasticity. After shrinkage in the longitudinal andtransverse directions by an average of 60%, this film shows only 1.2% ofincrease in Haze compared to a large value of 3.6% shown by the filmformed solely of SBC. Further, the heat seal strength at a hightemperature of 80° C. which this film shows is 1.2 kg/15 mm width, avalue definitely large compared with the value of 0.2 Kg/15 mm widthshown by the SBC layer.

Compared with the films obtained by the method of this invention theshrink films of vinyl chloride and polypropylene available in the marketshow inferior physical constants as will be dealt with afterward.Typical physical constants they show are 0.5 of and 1.9 Kg/15 mm widthof heat seal strength, 66° C. and 120° C. as temperature for 20%shrinkage, and 16 and 8 Kg.cm of dart impact strength.

Now, the film possessing barrier property which constitutes one of theobjects of this invention will be described. For the sake of simplicity,the barrier layer used in the film will be referred to as Br and theadhesive layer as CH. Then, possible combinations of component layersare as shown below (the component layers to be indicated in theincreasing order of distance from the outermost layer).

For the two-layered films, a typical combination of component layers isSBC/Br. In this layer combination, when emphasis is placed onshrinkability of the film, the thickness ratio of SBC/Br is desired toexceed 2/1. For example, the ratio may be suitably selected in the rangeof from 3/1 to 6/1.

For the three-layered films, typical combinations of component layersare SBC/Br/SBC, Io/Br/SBC, Io/Br/Io, and so on.

For the four-layered films, typical combinations of component layers areas follows:

(a) SBC/CH/Br/CH/SBC, EVA/SBC/Br/SBC/EVA, Io/SBC/Br/SBC/IoPP/SBC/Br/SBC/PP, PP/SBC/Br/SBC/Io, Ny/Io/SBC/Br/SBC, PP/CH/Br/SBC/Io,SBC/Br/SBC/CH, etc.

(b) SBC/PB/Br/SBC, SBC/PB/Br/CH, Io/SBC/PB/Br/EVA, SBC/PB/Br/PB/SBC,SBC/Br/PB/Br/SBC, PP/PB/Br/PB/PP, PP/PB/SBC/Br/SBC, Ny/Io/SBC/Br/SBC,etc.

For example, there can be produced a three-layered film of aconstruction consisting of the layers of SBC/PDC/SBC, namelyincorporating one inner Br layer formed of PDC and two outer layer eachformed of SBC. In this film, as produced in Run No. 12 of Example 4 ofthis invention, the layers have 14 and 6.5 and 21.5μ respectively ofthickness. As will be dealt with afterward, this film exhibitsoutstanding properties and high barrier property (45 CC/m².day.atm. ofO₂ permeability) and also shows high shrinkability at low temperatures.

The five-layered film of a construction consisting of the layers ofIo/SBC/PDC/SBC/Io as produced in Run No. 14 of Example 4 of thisinvention is a particularly good shrink film possessing high barrierproperty.

The films of the present invention are characterized by possessing highoptical properties such that the value of Haze (as determined by themethod specified by ASTM D1003-52) does not exceed 4.0%, preferably3.0%, and more preferably 2.0%. The Haze value stated here is thestandard means to be applied to films of an average thickness of 20μ. Itdoes not apply, therefore, to films which have great thicknesses orwhich have been tinted, embossed or dusted.

The outstanding transparency and the high strength properties which thefilms of this invention exhibit are ascribable to the fact that thecombinations of polymers involved can be efficiently molded withabsolutely no adverse effect upon their advantageous properties derivedfrom the quenching given in the course of sheet extrusion. It can alsobe ascribed to the fact that, even in the range of very low temperaturesnot exceeding the melting points, preferably the softening points, ofthe principal polymers involved, the film can be drawn very stably owingto the synergistic effects brought about by the combination of thecomponent resins. The fact that the synergistic effects of thecombination of the component polymers permit the film to be efficientlyprocessed without entailing any structural defects such as voids may beone possible cause. The films produced solely of PP or PB as in thecomparative examples can never achieve the aforementioned advantages.

The films of the present invention are further characterized by theirorientation characteristics being freely varied as by modifying themanner of cold drawing, i.e. causing the film to be drawn uniaxiallyonly in one of the longitudinal and transverse direction instead ofbeing drawn biaxially, by subjecting the film to a heat treatmentsubsequently to the biaxial drawing, or by changing the combination ofcomponent polymers. It is nevertheless desirable to have the film drawnbiaxially so far as the circumstance permits. The film thus producedexcels in heat shrink properties and, therefore, manifests outstandingproperties when used as a heat shrink film.

The fact that the temperature at which the film is allowed to undergoheat shrinking is low constitutes one of the necessary and importantfactors for the film to be used advantageously as a shrink wrappingfilm. This property is called low-temperature shrinking property. Thefilm which has another layers composed of PET, Ny and the like andprepared by heat setting is advantageous for use which does not utilizethe shrinking property of the film. When the film is tested for itsthermal shrinkage at each temperatures, the low-temperatureshrinkability is expressed by the value of temperature which is requiredfor the purpose of obtaining a specific amount of shrinkage of 20% or40% (to be expressed by an average shrinkage in the longitudinal andtransverse directions). The lower the value of this temperature, thebetter the low-temperature shrinkability. Generally, the shrinkage whichthe film to be used for shrink wrapping is required to possess is notless than 20%, preferably not less than 40%. To be specific, the thermalshrinkage is obtained by a procedure of preparing a square test piececut from a given film, inscribing a longitudinal and a transverse markeach of a specified dimension on the test piece, sprinkling the testpiece with a powder such as of talc so as to repress its surfacetackiness which often impedes convenience of handling, treating it withhot air of a prescribed temperature for five minutes for thereby causingthe test piece to shrink, and finding changes in the longitudinal andtransverse dimensions of the marks. The thermal shrinkage is expressedby the average of the longitudinal and transverse shrinkage. Thisthermal shrinkage is found at each temperature. The temperatures atwhich the film gives 20% and 40% of thermal shrinkage are reported astemperatures for shrinkages of 20% and 40% respectively.

In the case of the film of this invention to be used for shrinkwrapping, the value of this temperature is low. As shown in FIG. 1 to bedescribed afterward, the commercially available PP film for shrinkwrapping has 120° C. as the temperature of 20% of shrinkage and 134° C.as that of 40% to shrinkage as indicated by the curve 5, whereas thefilm of this invention has 52° C. as the temperature for 20% ofshrinkage and 70° C. as that of 40% of shrinkage as indicated by thecurve 1. Although this value is affected secondarily by the stretchingtemperature and the composition, the fact that this value is on a lowlevel constitutes one of the characteristics of the cold drawing of thepresent invention. If this value is high, required thermal shrinkage isnot effected unless the film is exposed at a fairly high temperature fora long time at the time of this actual use. Since the magnitude of heatgenerated by the heater must be increased, consequently, the speed ofthe packaging operation is lowered. Further, there is a possibility ofthe heat being transferred to the commodity being packaged. Suchtransfer of heat proves undesirable particularly where the commoditybeing packaged is highly vulnerable to heat, degradable or deformable bythe action of heat such as fiber or fresh food. In the case of a filmwhose curve of shrinkage tends to rise sharply at high temperatures, thefilm's shrinkage is heavily varied even by a very slight change near theshrinkage temperature at the time of packaging. When the film is looselywrapped around a commodity in advance and the loose package issubsequently passed through a shrinkage tunnel, a slight shortage in theoverall temperature of the hot air blown against the film results ininsufficient shrinkage, so that the film fails to come into skintightcontact with the contour of the commodity. If the temperature isslightly higher, the film is fused and sustains rupture or it isdeprived of transparency and optical homogeneity.

If the value of this temperature is extremely low, the film wound up ina roll suffers a dimentional change even at normal room temperature. Thecommercially available PVC plasticized film to be used for shrinkwrapping has 58° C. for 20of shrinkage and 88° C. for 40% of shrinkageas indicated by the curve 4 in the graph of FIG. 1. This suggests thatthis film possesses desirable low-temperature shrinkability, theshrinkage property varied smoothly with the temperature.

In the case of the shrinkable film which forms one of the objects of thepresent invention, this value for 20% of shrinkage is generally below85° C., preferably below 75° C. and more preferably below 70° C.

To date, no other commercially available film than the plasticized PVCfilm has had such desirable shrinkage property and strength.

The film which forms one of the objects of this invention has beenobtained by using other resins than the PVC. It excels the PVC in termsof the responsivity to shrinkage and, in this respect, defies allcomparisons. The thermal shrink tension exhibited at the time ofshrinkage constitues one of the important thermal shrinkage properties,comparable with the thermal shrinkage which is an important factor whenthe film is used for the purpose of shrink wrapping.

For example, even if the thermal shrinkage is high, the film fails tofit tightly to the commodity being packaged during or after the step ofpackaging when the tension generated in the film at the time ofshrinkage is low or deviates in the direction of higher temperatures aswill be described afterward. The film, then, fails to produce desiredbinding force and can no longer serve for the purpose of shrinkwrapping.

If the value of this tension is insufficient even to the slightestextent for the purpose of producing binding force (value of shrinkstress), the film is required to have its thickness increased to make upfor the insufficiency. Such increase in the film thickness isuneconomical and inconvenient. Generally, this maximum value is desiredto be not less than 50 g/mm², preferably not less than 80 g/mm², morepreferably not less than 100 g/mm², and most preferably not less than150 g/mm². As shown in FIG. 2, the commercially available polyethylenefilm for shrink wrapping has a thermal shrink tension of not more than10 g/mm² and about 5 g/mm² as indicated by the curve 7. Thus, the filmis applicable to limited uses. The film of this invention has a value of200 g/mm² as indicated by the curve 1 in the same graph. Generally, thefilm of this invention has a sufficiently high value in the range offrom 100 to 400 g/mm².

In the case of the low-temperature shrinkable film, this shrink tensionis not significant unless it is manifested at a temperature close to thetemperature corresponding to the shrinkage. The temperature-dependencycurve of the shrink tension must be well balanced with theshrinkage-temperature curve (expressed by the average of the values forlongitudinal and transverse directions). At times, the thermal shrinktension is desired to occur in an increased range of temperatures. Inthis respect, the film of the present invention can be adjusted byproperly selecting the composition and treatment.

In the present invention, the stiffness of the film can freely beadjusted in the range of from fair softness to considerable regidity byvarying the combination and thickness distribution of specific polymerlayers, the compositions of the resins, etc.

The film of the present invention is further characterized by possessinga particularly high tensile strength. The strength at rupture, reportedas the value found in the direction of drawing or in at least one of thelongitudinal and transverse directions of drawing or preferably as theaverage of the values found in the longitudinal and transversedirections, is at least 5 Kg/mm² (as determined in accordance with themethod of ASTM D-882-67), preferably not less than 7 Kg/mm². Theelongation at rupture is desired to be not less than 100%, preferablynot less than 150%, and more preferably not less than 200%. The dartimpact strength is determined by following the method of ASTM D-1709-67with necessary modifications. It is expressed by the value which isobtained by using a special dart whose missile head is provided with agrooved edge to facilitate rupture of the film. The film of thisinvention is also characterized by the fact that value of its dartimpact strength is particularly high. For example, while the PVC filmand the PP film have the values of 16 and 8 Kg.cm respectively, the filmin the Run No. 4 has as high a value as 37 Kg.cm (as expressed on thebasis of 17μ of thickness), which is comparable with the value obtainedby heavy bags of LDPE 100 to 150μ in thickness available on the market.The dart impact strength is generally not less than 15 Kg.cm, preferablynot less than 20 Kg.cm (as expressed on the basis of 17μ of thickness).

The fact that the tensile strength is high and the elongation is greatas described above means that the film is tough and highly resistant totear. Thus, the film proves highly advantageous for the protection ofarticles being packaged and permits a reduction in the film thickness.

The film of this invention possesses a strength at rupture of 16.5Kg/mm² and an elongation of 210% as shown afterward in Run No. 9.Generally, when the strength is enhanced by orientation, the elongationof the film tends to decrease to an extreme extent. In the case of thecommercial film which is formed solely of LDPE and thoroughlycrosslinked (with the insoluble gel content in boiling xylene brought to67% by weight) and consequently oriented sufficiently as described inComparative Example (c) afterward, the strength is 6.9 Kg/mm² and theelongation is 45%, indicating that the film is highly liable to rupture.The use found for the film of this invention is not limited shrinkwrapping. By virtue of its excellent toughness, it can be utilizedwidely as an industrial film.

By the after-treatment restoring to heat setting, the temperature forthermal shrinkage, the orientation balance in the longitudinal andlateral directions and the stabilization of the film for shrinkage canfreely be adjusted so as to adapt the film of this invention for otheruses or enable the film to be laminated with various other films.

Barrier layers can be made of PVDC type resin, nylon type resin,polyester type resin, resin of saponified EVA and the like. By suitableselection of the combination of resins, the number of layers and thethicknesses of individual layers, there can be advantageouslymanufactured a low-temperature shrinkable film bag of desired barrierproperty. A film suitable for use as heat-resistant retort requiring nolow-temperature shrinkability can be produced, for example, by givingthe film a specific heat treatment, selecting the combination ofpolymers or subjecting the film to heat setting. Besides, films havingthe properties thereof suitably modified by chemical reactions such ascrosslinking, grafting, etc. can be manufactured without any specificrestriction.

One preferred example of the process of this invention for theproduction of a film from the combination of specific polymers will bedescribed in detail herein below.

The process of the present invention comprises thermally meltingsuitably selected specific polymers in each extruder, extruding themolten polymers directly through a multi-layer die or joining the moltenpolymers in front of a die and then extruding them through the die orextruding the molten polymers one after another into resin films so thatthe successive resin films are piled up one on top of another and,thereafter, suddenly solidifying a resultant multilayered sheet with aliquefied refrigerant to produce a tubular or flat raw sheet or film ofsufficient uniformity. It is desirable in this case to have theindividual layers of polymers simultaneously extruded to give rise to atubular multilayered raw sheet or film. The tubular raw sheet or filmthus produced may be subjected to crosslinking by means of an energyray.

The resultant sheet or film which contains at least one layer formed ofSBC, PB-1 or Io is cold drawn at a temperature within the range of from20° to 80° C. to an area stretching ratio within the range of from 3 to30 times. The temperature at which the sheet or film is drawn asdescribed above is the temperature at which the drawing of the sheet isstarted.

Now preferred embodiments of the present invention will be described. Itshould be noted that the present invention is not limited to theseembodiments in any way.

The extrusion is effected at an extruding temperature within the rangeof from 150° to 280° C. through a multi-layer annular die which isadapted effectively to avoid giving to the extruded sheet uneven wallthickness or imparting thereto heat and time hysteresis. The extrudedtubular raw sheet or film is suddenly solidified by having its outerperiphery uniformly cooled with a liquefied coolant to give rise to athoroughly homogenized tubular sheet or film (in terms of both shape andinner texture). Optionally this tubular sheet or film may be pre-treatedwith a high-energy ray such as, for example, an electron ray, gamma rayor ultraviolet ray. The pre-treatment can be advantageously carried outby use of an electron ray having a dosage of 1 to 10 Mrads, for example.This treatment, if carried out to any excess, produces adverse effectson the various properties of the produced film.

The subsequent step of drawing is carried out either at normal roomtemperature or at an elevated temperature by application of heat. Inthis case, the temperature at which the drawing is carried out must bekept below the level at which the main crystals in the principalpolymers in the sheet, preferably the main crystals in all the layersmaking up the sheet, are melted (which temperature is measured at thescan speed of 20° C./min. at the peak value stated in accordance withthe DCS method). This is because once the crystals are melted, they arerecrystallized at a temperature considerably lower than their meltingpoint and this difference between the two temperatures increases inproportion to the speed of temperature increase or decrease, so that thesheet cannot be given practically ample cold orientation. This trend isparticularly conspicuous in the case of the ionomer resin. In the caseof the Na-crosslinked resin formed of ethylenemethacrylic acid copolymerhaving a methacrylic acid content of 5.4 mol%, MI of 1.3 and a densityof 0.942 g/cm³, the temperature of crystallization measured at a scanspeed of 20° C./min. (while the actual film-forming speed is muchhigher) at times has its peak at 50° C. despite the fact that theinherent peak melting point is 100° C. The trend described above doesnot apply, however, where the overall degrees of crystallinity are low.

Generally in the present invention, the drawing is desired to be carriedout at a very low temperature of not more than 80° C., preferably in therange of from 20 ° to 70° C., and more preferably in the range of from20° to 60° C. It is further desirable that the drawing is performedbelow the Vicat softening points of the specific polymers used in thefilm. To be specific, the drawing temperature is desired to be 10 ° C.,preferably 15° C., lower than the Vicat softening points. To enhance theproperties of the film, the drawing is desired to be carried out at thelowest possible temperature that is tolerated from the standpoint of thestability of processing. When the drawing is made at a temperatureexceeding the upper limit indicated above, the various properties of thefilm are sharply degraded and, at the same time, the stability ofdrawing is impaired and the uniformity of film thickness and thestability of bubble are jeopardized. Besides, the low-temperatureshrinkability and the shrinkage gradient are adversely affected andvarious other properties such as optical properties, strengthproperties, elongation and resistance to pinholes (in the case ofbarrier layers) are seriously impaired. The inflation of the tubularsheet into a bubble in the course of drawing under application of heatis desired to be carried out with the current of air sweeping thesurface layer of the bubble regulated as uniformly as permissible byadjusting the blowing of air by means of an air ring. The heating of thesheet, in this case, is desired to be kept within 20° C. above thetemperature at which the drawing is started. This regulation of thetemperature is imperative, because the zone of the air ring which risesto the highest temperature is suffered to swell out particularly at thestart of the heat application when the temperature for the heating ofthe sheet is more than 20° C. above the starting temperature.

More often than not, the stretching zone through which the sheet isdrawn is desired to be heated with a temperature gradient such that thetemperature at the starting portion of the zone differs by at least 5°C., preferably 10° C., from that at the terminating portion.

To smoothen the drawing, the flow of the fluid medium (such as air)sweeping the surface layer of the tubular sheet being drawn iscontrolled by the following method. The control may be effected by someother suitable method to suit the occasion. For the purpose ofestablishing a suitable temperature distribution through the entiredrawing zone, there are adopted contact guides whereby the drawing iscarried out while the fluid being entrained by the surface of the sheetor film in motion and fluid (fluid film) on the surface of the sheet orfilm can be removed in the circumferential directions by virtue of thefluid's discontinuous contact with the guides. Particularly when theheating zone and the starting portion of the drawing zone aresubstantially isolated from each other by means of the aforementionedcontact guides, the otherwise possible uneven drawing can be precludedowing to the mutual thermal interactions among the heating zone, thestarting portion of the drawing zone and the cooling zone. This methodcan be applied similarly to the starting portion of the drawing zone,the drawing zone and the terminating portion of the drawing zone. Thedrawing is desired to be effected to a full extent by keeping the innerpressure of the bubble at a high level of 100 to 5000 mm H₂ O,preferably 200 to 2000 mm H₂ O, (as measured on the basis of a sheet200μ in thickness and 100 mm in diameter).

As regards the extent of drawing, the area stretching ratio is desiredto fall within the range of from 3 to 30 times the original dimension,preferably from 7 to 20 times the original dimension, and the transverseexpansion ratio within the range of from 2 to 7 times the originaldimension. More preferable ranges are 7 to 20 times for the areastretching ratio and 2 to 5 times for the transverse stretching ratiorespectively. At this time, it is important that the sheet is producedwith ample homogeneity as mentioned previously. If the wall thickness ofthe sheet involves a deviation close to or in excess of ±10%, forexample, the sheet may sustain puncture and can no longer be effectivelydrawn. The deviation of the wall thickness of the sheet is desired to bewithin ±5%, preferably within ±2%. The extent of the drawing can beadjusted most advantageously by first fixing the drawing ratio in thelongitudinal direction by selecting the speed ratio between the feed niprollers and the takeup nip rollers and subsequently introducing air intothe bubble and causing the bubble to inflate close to the end point ofdrawing (immediately preceding the point at which the sheet begins toblush) and eventually cease to inflate in the transverse direction. Thisis an ideal method for effecting the drawing of sheet most stably. Themachine used for drawing the tubular sheet, because of the peculiarrelation between the inner pressure and the diameter of the bubble, isdesired to have as large a diameter as possible, generally greater than50 mm, preferably greater than 100 mm. In due consideration of thephysical properties of the film to be produced, the drawing is desiredto be performed at an amply low temperature tolerated from thestandpoint of the stability of the bubble. For practical purpose, itsuffices to determine the extent of drawing on the basis of thecomposition of polymers being used, with due consideration paid to thebalance with the stability of the bubble (enough to preclude possiblefilm puncture). Owing to the small heat transfer which characterizes theprocess of the present invention, the total thickness of the film can befreely selected from a wide range of from a very small order of 3 to 5μto a very large order of 100 to 150μ. The generous choice of the filmthickness afforded by the present invention has never been attained withany of the conventional films.

The film which is obtained by the process of this invention acquires theoutstanding properties mentioned above and, more often than not, has ahighly limited deviation of film thickness of the order of ±5% or evenless after the step of drawing. A possible reason for this advantage isthat the high inner pressure applied to bear upon the bubble imparts astrong drawing force to the film and the heat hysteresis generallyinvolved in the course of heating and cooling is notably small and,consequently, the film enjoys high uniformity and stability. The opticalproperties (both Haze and gloss) of the tubular sheet appear to be quiteinferior. They are notably improved, however, after the tubular sheethas undergone the treatment for cold drawing by the process of thisinvenion. Also because of the multi-layer construction, the stability ofmolding of the film is notably improved as compared with thesingle-layer film. Thus, the process of this invention is capable ofproducing products of uniform and high quality.

In the present invention, the component polymers which make up the filmare allowed to manifest their respective synergistic effects becausethey are used in the form of multiple layers in the film. None of thecomponent polymers used in the film either brings about a drawback ofthe kind often experience in a similar situation or causes anydegradation of strength. This advantage of the present invention isnever attained by the ordinary drawing process which requires the sheetto be heated to or over its melting point. In the case of theconventional film produced by the ordinary drawing process, the drawingtemperature must be elevated to have the optical properties of the filmimproved. Use of the elevated drawing temperature renders the desiredorientation all the more difficult and tends to degrade the filmstrength.

The same thing also applies to the ordinary drawing process which uses adrawing temperature 5° to 10° C. more or less than the melting point. Atsuch a drawing temperature, the optical properties of the film obtainedare far from being satisfactory and, in the case of a mixed composition,the temperature conditions are such as to embrittle the tubular sheet toan intolerable extent. Thus, the film sustains puncture and fails toacquire advantageous properties in most cases. As demonstrated in thepreferred embodiment of this invention cited afterward, the cold drawingaimed at by the present invention can be effectively attained at a verylow temperature such as, for example, 32° C. This is an unprecedentedachievement. It is never materialized unless the synergistic effectspeculiar to this invention are derived from the uniform sudden coolingof the multi-layered tubular sheet including a specific layer such as ofcold drawable resin and the fulfilment of the conditions essential forthe specific drawing.

In the case of the single-layer film formed solely of PP, for example,the drawing is obtained continuously barely at a temperature fallingwithin a very small range of from 140° to 160° C. under difficult anddelicate conditions. At a lower temperature, the film sustains punctureand is incapable of continued drawing. At a higher temperature, there isobtained a blushed, weak film of inferior properties. With theconventional film, absolutely no effective drawing has been obtained attemperatures in the neighborhood of 80° C., let alone the extremely lowtemperature of 32° C. at which the film of the present invention can bedrawn as described above. This outstanding cold drawability of the filmof the present invention is really amazing.

Further, the properties of the film produced by this invention,including strength, optical properties, low-temperature shrinkability,seal property, tear strength and, among others, impact strength farexcel those exhibited by the single-layer film. The drawing by thepresent invention can be effected to a level decisively higher than thelevel obtained by the ordinary drawing process.

The same thing applies to the film of this invention which incorporatesadditional layers made of resins other than the resins embraced by thisinvention. With the film of this invention, biaxial drawing can beaccomplished at an extremely low temperature which departs far from thescope which finds general approval.

When the film is subjected to the biaxial drawing, the layers such as ofSBC, PB, and Io have their drawing conditions and film propertiesnotably improved owing to the synergistic effects produced by theinteraction of the resins embraced by this invention and other resins.These layers, at times, function as adhesive layers.

When rolls of the film of this invention are put to storage in a roomkept at normal room temperature, for example, there is a possibilitythat the rolls piled up in a heap will slip and fall down as a result ofchange of size in the film. With a view to preventing this trouble, thefilm which has been drawn may be subjected to a heat treatment while itis still on line or after it has been wound up in rolls, so that thefilm is stabilized dimensionally and, consequently, freed from thefactor responsible for shrinkage at normal room temperature. Thistreatment, if performed to a suitable extent, permits free control ofthe aforementioned factor without impairing the other properties. Thistreatment also enables the orientations already set in a biaxially drawnfilm to be freely shifted in the longitudinal and transverse directions.

The total thickness of the raw sheet or film can freely be selectedgenerally in the range of from 20-30μ to 2-3 mm. More practically, therange of thickness is from 50 to 1000μ.

The composition and the combination of layers according to the presentinvention can be applied to films monoaxially drawn to a high degree.They are similarly applicable to films of low orientation which areproduced by extruding the resins, inflating the extruded sheets andsuddenly cooling the inflated sheets. Further, since the films using thecomposition and the combination of specific polymers according to thisinvention are readily cold drawn at normal room temperature, they can beadvantageously utilized as films of high strength properties (such as,for example, tensile strength, tear resistance, impact resistance) andfilms excelling in heat seal property, modulus of elasticity, surfaceproperties (hardness, freedom from smear, excessive slipperiness,frosting, etc.), heat resistance and barrier property.

Now the film and the process for the manufacture of the film accordingto the present invention will be described specifically with referenceto working examples of the invention. It should be noted that thisinvention is not limited to these examples.

EXAMPLE 1

60% by weight of EVA (a₁) [the vinylacetate content (VAC) 10% byweight=(3.5 mol%), the melt index (MI) 1.0, the Vicat softening point(VSP) 75° C., the crystal melting point (MP) 95° C.] and 15% by weightof the ethylene-α-olefin copolymer elastomer (b₁) (α-olefin ispropylene, said copolymer was obtained by the random copolymerization of18 mol% of propylene and 2% by weight of ethylidine norbornene) havingMI of 0.45, VSP of not more than 40° C. and the density of 0.88 g/cm³were mixed with 25% by weight of IPP (C₁) [the melt flow rate (MFR) of2.0, the density of 0.88 g/cm³, said IPP copolymer comprises 3% byweight of ethylene] having VSP of 143° C. and MP of 155° C. in theblender to produce the mixed resin composition as the resin for theSBC₁₁₁ layer use. And then the ionically crosslinked resin (Ionomer)(E₁) (said resin was manufactured by 30 % neutralizing the saponifiedpolymer of the ethylene-methyl methacrylate copolymer in the presence ofNa⁺ ion, the methacrylic acid content 20% by weight) having MI of 1.0,VSP of 62° C. and MP of 83° C. was used as the Io layer. Said mixedresin composition and said ionically crosslinked resin (E₁) were mixedat the maximum temperature of the cylinder part of 240° C. by each twoof the extruders having 40 mm in diameter provided with the screw havingthe ratio (L/D) of 33 respectively to produce the plasticized kneadingcompositions and said compositions were co-extruded from two sorts ofthree layered annular die 100 mm in diameter having the slit of 2.5 mm.Then the extruded product was quenched at the position which was about10 cm distance from the lip of the die by the water-cooling ring fromwhich water of 8° C. was uniformly flowed out.

Thus there was obtained the raw tubular film 100 mm in diameter, andhaving the first layer (the outer layer) of the Io layer, the secondlayer of the SBC₁₁₁ layer and the third layer of the Io layer inthickness as shown in Table 1.

The raw tubular film was passed between the two pairs of the deliverynip rolls and the draw nip rolls which rotate faster than the deliverynip rolls respectively, while passing said rolls, the raw tubular filmwas heated to the temperature of 37° C. by the hot air and then wascontinuously inflated by blowing air into the tubular film and stretchedby 3.0 times in the longitudinal direction and 3.5 times of thetransverse direction with good stability.

The cold air of 12° C. was blown to the film from the air ring apparatusat the end of the stretching step to cool the film. The film was foldedup by the deflator and then taken up by the nip rolls and serarated tothe two sheets of film by slitting the edges of the film in thelongitudinal direction. Each of which was wound up under the certaintension and the films having the predetermined thickness were obtained.In order to highly stretching the film smoothly, the contacting guidefor conditioning the flow of the film was used for the purpose ofsubstantially separating the heating part and the beginning part of thestretching step thereby discontinuously contacting with the surface ofthe raw film and the stretching film and removing in the circumferencedirection, the fluid being entrained by the surface and fluid on thesurface of the film which were accompanied with the raw film and thestretched film on the surface thereof. And then while stretching, saidcontacting guide was also used in the bubble part whereby the individualtemperature controled rooms were substantially formed. Thus whileelongating and stretching the film, said temperature controlled roomswere step-wisely formed on the surface of film thereby making itpossible to stretch with high stability by zone-controlling. Table 2showed the characteristic properties of the resulted film in comparisonwith those of the commercial three sorts of the shrink films.

                  TABLE 1                                                         ______________________________________                                                                       (Com-                                          Combination                    parative                                       in thickness                                                                           Run No.               Example)                                       of raw film                                                                            1      2      3    4    5    6    1    2                             ______________________________________                                        First layer                                                                            50      5      15   6    20   50  --   150                           (μ)                                                                        Second layer                                                                           50     120    170  188  460  600  200  --                            (μ)                                                                        Third layer                                                                            50      5      15   6    20   50  --   --                            (μ)                                                                        Total thick-                                                                           150    130    200  200  500  700  200  150                           ness (μ)                                                                   ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________                                          (Comparative                                                                          (Comparative                                  Run No.                 Example)                                                                              Example)                        Characteristics                                                                             1   2   3   4   5   6   1   2   a   b   c                       __________________________________________________________________________    Haze (%)      0.5 0.6 0.6 0.5 0.7 0.8 1.4 0.9 1.7 2.8 2.5                     Gloss         150 165 155 160 155 150 130 153 123 105 103                     Thermal                                                                            20% shrinkage                                                                          52  55  53  55  54  55  60  51  58  120 100                     property                                                                           temperature (°C.)                                                      Maximum  76  77  75  78  77  76  74  64  57  72  76                           shrinkage (%)                                                                 Shrink tension                                                                         200 210 220 215 230 235 200 145 97  209 150                          (g/mm.sup.2)                                                             Tensile strength (Kg/mm.sup.2)                                                              12.0                                                                              12.5                                                                              11.5                                                                              13.5                                                                              13.0                                                                              12.5                                                                              11.5                                                                              9.5 6.0 12.0                                                                              6.9                     Tensile elongation (%)                                                                      200 250 245 235 215 240 220 180 140 110 45                      Modulus of elasticity                                                                       41  38  36  40  38  36  33  30  32  80  40                      on tensile (Kg/mm.sup.2)                                                      Dart impact strength                                                                        30  29  35  37  34  35  24  14  16  8   8                       (Kg · cm)                                                            Heat seal strength                                                                          1.1 1.8 2.2 1.9 4.1 5.5 1.1 1.5 0.5 1.9 (0.3)                   (Kg/15 mm width)                                                              Film thickness (μ)                                                                       15  12  19  18.5                                                                              47  67  17  22  15  15  17                      __________________________________________________________________________

Note: Gloss was measured in accordance with ASTM 2454-65T. Heat sealstrength was measured using the sample which was sealed by thecommercial melt-cutting type heat-sealer. Modulus of elasticity ontensile was the value changing the modulus at 2% elongation into that at100% elongation and measured in accordance with ASTMD 822-67.

The comparative sample (a) is commercial PVC shrink film.

The comparative sample (b) is commercial PP shrink film.

The comparative sample (c) is commercial crosslinked polyethylene shrinkfilm (gel content 67%).

Run Nos. 1-6 were stretched with good stability without observing anysway of the bubbles. Stretching was carried out without accompanying anyproblem. The comparative sample Run Nos. 1 and 2 were the single layerfilm to be stretched. When stretching the film, the bubble sustainedpuncture two times in an hour in the sample Run No. 1, and four to fivetimes in the sample Run No. 2 and the bubble was apt to sway and alsothe stretching was apt to stop in the low stretching ratio.

The obtained films had the good characteristic properties and weresuperier to those of the comparative films (a), (b) and (c).

Comparing 20% shrinkage temperature, the comparative PVC film (a) hadlow temperature and the comparative PP film (b) had high temperature of120° C., while the film of the present invention had the temperature of52°-55° C. and had the characteristic property like or over that of thePVC film and also was superior to the comparative PVC film (a) in theshrink tension, the tensile strength, especially the heat seal strengthand the impact strength.

In the practical test of wrapping four cucumbers, wrapping was carriedout by passing the wrapping film Run No. 2 for 2 seconds through theconventional tunnel oven which blew the hot air of 90° C. to thecucumbers thereby obtaining the good wrapping finish tightly fitted withthe cucumbers and not having any wrinkle and not depressing good opticalproperty after shrinkage. From the test result, it was found to be ableto smoothly carry out good wrapping at the broader range of the heatingtime with the broader speed range from the low temperature side.

While, the commercial shrink film of polypropylene did not almost shrinkat 90° C. in 10 seconds and remained the wrinkle on the sample, thesatisfactory shrinking could not be accomplished without the highshrinkage temperature of 170° C. in 5 seconds under the same conditionas mentioned above. Even if the heating temperature was further raisedand the staying time was prolonged, the wrapping film was broken due topitting and became opaque. The optimum shrinkage temperature range ofthe film was very narrow. The commercial shrink film of PVC had lack ofthe shrinkage and remained the wrinkle under the same wrapping conditionas mentioned above. Therefore, the shrinkage temperature of 150° C. in 5seconds was required. The shrinkage rate of the film of the presentinvention was especially fast and could be wrapped within one second.

The shrink film of the commercial crosslinked polyethylene was notsuitable as the wrapping film since it could not shrink without the hightemperature of 170° C., so that the good wrapping finish was notobtained. The film was easy to break at the sealed part and moreover,was apt to occur much breakage, the good wrapping range of the film wasjudged from the shrinkage, the binding force, the hole at the sealingpart, the rupture from the air vent part and the devitrificationphenomenon of the film after wrapping. Furthermore, judging from thegood wrapping finish, the film of the present invention was the bestone.

And, in order to examine the shrinkage rate or speed of the film of thepresent invention, the film of the present invention and those of thecomparative samples (a), (b) and (c) were entered into the air ovenwhich was controlled to the various temperatures and then theinterrelationship between the temperature and the time was examined whensaid films reached to 40% shrinkage. From the test result, saidinterrelationship was 2 seconds at 90° C. in the film of the presentinvention, 2 seconds at 170° C. in the comparative sample (a), 2 secondsat 200° C. in the comparative sample (b), and 2 seconds at 180° C. inthe comparative sample (c) respectively. It was found that the film ofthe present invention had the good shrinkage speed. After shrinkage, thechange of the optical property about the films of present invention andthe comparative samples were examined. The test result at 40% shrinkageshowed that the films of the present invention Run No. 2, thecomparative sample Run Nos. 1, 2, (a), (b) and (c) had the Haze of 0.8,2.8, 3.0, 1.8, 3.1 and 4.9% respectively, and that the film of thepresent invention had the most superior optical property. The gloss ofsaid films were 160, 100, 128, 110 and 87 respectively. After shrinkage,the depression of gloss was few. The sealing strength of the film of thepresent invention was strong in spite of the thin film and was apt to bestronger than the single layer films of the comparative samples Nos. 1and 2 respectively. The sealing strength of the PVC film of thecomparative sample (a) was low of 0.5 kg/15 mm width. Said samplegenerated gas with the bad odor and remained the darkish cinders in thesealing part when heat-sealed, and formed the unstable sealing, while inthe comparative sample (c), the heat-sealing could not be smoothlycarried out owing to the high crosslinkage and the good cut was notobtained.

The sealing strength of the films of the present invention Run No. 2 andthe comparative samples Run Nos. 1, 2, (a), and (b) at the temperatureof 80° C. was 0.6, 0.12, 0.17, 0.04 and 1.1 kg/15 mm width respectively,(in the practical wrapping, the sealing temperature is more than 80° C.)

The film of the present invention Run No. 3 had the broader range of theoptimum wrapping temperature than that of the comparative samples RunNos. 1 and 2. Especially, the film of the comparative sample Run No. 2was devitrification when passing it through the tunnel oven of 140° C.for 6 seconds and had lost the shrink tension whereby the film gotloose, while the film of the present invention Run No. 3 had good heatresisting property and was not observed such phenomenon as mentionedabove.

Hereafter, the strength, the elongation and the heat-shrinking propertyof the film were shown by the mean value between those of thelongitudinal and transverse directions since said characters of the filmhad in the longitudinal and transverse directions in good balance.

EXAMPLE 2

The raw tubular three layer film was manufactured under the process ofExample 1 using the middle layer (the 2nd layer) of the crystalline PB-1(d₁) (MI 1.0, the density of 0.905 g/cm³, the butene-1 unit content 96mol %, VSP 108° C. and MP 135° C.) and the inner and outer layers (thefirst and the third layers) of IPP (C₂) (MFR 6.0, the ethylene content5% by weight, the density of 0.88 g/cm³, VSP 145° C. and MP 150° C.) inthe composite ratio of Table 3.

This film was heated and stretched under the condition of Example 1 atthe temperature of 30° C. The result was shown in Table 4.

                  TABLE 3                                                         ______________________________________                                        Combination                   (Comparative                                    in thickness of                                                                           Run No.           Example)                                        raw film    7     8      9    10   11   3    4                                ______________________________________                                        First layer (μ)                                                                         5     15     30   50   50  --   100                              Second layer (μ)                                                                       70    170    140  100  400  200  --                               Third layer (μ)                                                                         5     15     30   50   50  --   --                               Total thickness (μ)                                                                    80    200    200  200  500  200  100                              ______________________________________                                    

From the result, it was found that the stretching could be smoothlycarried out on the films of the present invention (Run No. 7-11). Whilethe film of the comparative sample Run No. 4 could not be stretched orblown up at all and sustained puncture. In the comparative film Run No.3, the inflation stopped at the ratio of 1.9 times in the transversedirection and when the inflation was proceeded, the film sustainedpuncture and also was unstable and showed bad sizing in the inflationstep.

                                      TABLE 4                                     __________________________________________________________________________                                         (Comparative                                              Run No.             Example)                                 Characteristics  7   8   9   10  11  3   4                                    __________________________________________________________________________    Haze (%)         0.5 0.8 0.6 1.1 1.4 25  --                                   Gloss            155 150 152 140 138 30  --                                   Thermal                                                                            20% shrinkage                                                                             54  57  62  65  58  83  --                                   property                                                                           temperature (°C.)                                                      Maximum     83  82  83  78  76  67  --                                        shrinkage (%)                                                                 Shrink tension (g/mm.sup.2)                                                               240 260 350 280 260 45  --                                   Tensile strength (Kg/mm.sup.2)                                                                 12.7                                                                              14.5                                                                              16.5                                                                              13.5                                                                              12.5                                                                              4.2 --                                   Tensile elongation (%)                                                                         160 170 210 180 190 30  --                                   Modulus of elasticity                                                                          35  42  52  65  34  11  --                                   on tensile (Kg/mm.sup.2)                                                      Dart impact strength (Kg · cm)                                                        32  38  42  28  26  14  --                                   Heat seal strength                                                                             1.8 2.6 2.8 2.7 3.9 0.35                                                                              --                                   (Kg/15 mm width)                                                              Film thickness (μ)                                                                          7   16  18  20  46  30  --                                   __________________________________________________________________________

The films of the present invention Run Nos. 7-11 were remarkably good inthe optical property and strength. The thin film of Run No. 7 was softand difficult to break in comparison with the commercial PP single film(b) 15μ in thickness. The film of the present invention had the hardsurface and was difficult to injure. The film of Run No. 8 had goodshrinking and wrapping finish without occuring any wrinkle on thefinishing surface under the wrapping condition of 100° C., 2 secondswhen the wrapping was carried out according to the wrapping operation ofExample 1.

The sealing strength of the films Run Nos. 7-11 at 80° C. showedsuperior values of 1.0, 1.2, 1.5, 1.9 and 2.5 kg/15 mm widthrespectively.

The raw film having the composition and combination as shown in Run No.8 was stretched at the stretching temperature of 88° C. but it could notbe stretched due to causing breakage of the film at fast stage. At thestretching temperature of 140° C., the film was somewhat inflated andimmediately after the inflation, the film sustained puncture. The saidfilm had good and stable properties at the low temperature range andbecome whitish on the surface of the film as the temperature increasesand also was apt to depress the low temperature shrink property and thestrength of the film. This phenomenon was deduced to be based on thedepression of the cold stretching property of the PB-1 (d₁) film and theloss of the synergistic effect between the surface layer of the film(PP) and the middle layer of (d₁).

At the low temperature at which the film of the present invention couldbe stretched, the PP single layer film of the comparative sample Run No.4 could not be stretched since it sustained puncture at the beginning ofthe inflation. It could be stretched with difficulty at the temperatureof 145° C. in the unstable state while maintaining the delicate balance.However, this film had the same character to that of the commercialshrink film. When the stretching temperature was raised to 160°-170°°C.,the stretchability became better but the obtained film became whitishand had the weak strength, while the film of the present invention hadgood low temperature shrinkage and did not show such the phenomenon asmentioned above.

In the film of the comparative sample Run No. 3, the PB-1 layer was inthe rubber like state for 6-7 minutes immediately after stretching andquenching the film and could be relatively easily stretched. But thisfilm became whitish at the surface of film and had the considerablyinferior properties in the low temperature shrinkage, the elongation andthe strength. However, it was found that the good highly oriented filmwas manufactured when the PB-1 film was combined with the another layerand then stretched. This was the surprising fact, especially, the saidcombination was enable to obtain the highly oriented film from the resinlayer which can not be stretched at such the low temperature asmentioned in the present invention whereby the film having good strengthwas obtained. This characteristic property was apt to disappear when thePB-1 layer was combinated with another resins layer except those of thepresent invention. The PB-1 layer was necessary to the demanded in theamount of more than 50% by weight. In case that the combination was forexample the PP layer of 53% by weight, the PB-1 layer of 33% by weightand the isotactic PP layer of 14% by weight instead of the second layerof the PB-1 layer of the sample Run No. 9, it was impossible to carryout the low temperature stretching.

EXAMPLE 3

The raw tubular film was manufactured according to the process ofExample 1, using the ionically crosslinked resin (Ionomer) (E₂) (Theresin was manufactured by the 30% nutralization of the 60% saponifiedpolymer of ethylenemethylmethacrylate, the methacrylic acid unit content18% by weight, MI 1.0, VSP 68° C. and MP 86° C.) as the Io layer, andthe EVA (a₂) (the EAC content 18% by weight (6.7 mol%), MI 1.0, VSP 63°C. and MP 82° C.) as the inner and outer layer. The raw tubular film hadthe combination of Io/EVA/Io layers 50/80/50μ in thickness. This filmwas stretched at the temperature of 45° C. The stretching was smoothlycarried out. The characteristic properties of the film as shown inTables 2 and 4 were 0.5%, 152, 50° C., 73%, 170 g/mm², 10.5 kg/mm²,240%, 22 kg/mm.sup. 2, 29 kg.cm, 1.9 kg/15 mm width and 17μ in order.

EXAMPLE 4

The raw tubular film was manufactured according to the process ofExample 1 under the operating condition of Table 5 optionally andadditionally using one of the extruder (the extruder for the vinylidenepolymer use having 35 mm in diameter and the ratio (L/D) of 22) andfurthermore one of said extruder in the total of four extruders and alsooptionally using the two sort and three layer die, the three sort andthree layer die, the three sort and five layer die, and the four sortand five layer die respectively.

Each of the raw film was stretched at the temperature of 35° C., 36° C.,42° C., 40° C., 45° C., 32° C., 50° C. and 36° C. respectively accordingto the process of Example 1. The stretching was smoothly accomplished onthe all films. The film of Run No. 19 was not contained the dustinginhibitor in the film and the blocking inhibitor in the inner layer ofresin in the manufacture of the raw tubular film respectively and wasstretched and wound up the roll and then was carried out the brocking inthe inner side of the raw tubular film to obtain the double layer film.Therefore, the film of Run No. 19 was the ten layer film. The filmsother than that of Run No. 19 were the tubular type bag.

                                      TABLE 5                                     __________________________________________________________________________    Combination of                                                                           Run No.                                                            thickness of raw film                                                                    12  13   14  15  16     17      18  19                             __________________________________________________________________________    First layer (μ)                                                                       SBC.sub.111                                                                       EVA(a.sub.1)                                                                       Io(E.sub.2)                                                                       Io(E.sub.2)                                                                       Io(E.sub.1) + Ny.sub.2                                                               PP(C.sub.2)                                                                           Ny.sub.2                                                                          Io(E.sub.1)                               150 50   50  120 *130   50      50  60                             Second layer (μ)                                                                      PDC-1                                                                             SBC.sub.211                                                                        SBC.sub.242                                                                       PDC-2                                                                             CH.sub.1                                                                             PB-1(d.sub.2) + a.sub.2                                                               Io(E.sub.1)                                                                       SBC.sub.11                                70  200  190 80  50     **190   120 50                             Third layer (μ)                                                                       SBC.sub.111                                                                       PDC-2                                                                              PDC-3                                                                             Io(E.sub.2)                                                                       PDC-1  PDC-2   CH.sub.2                                                                          PDC-1                                     230 100  60  300 100    80      50  50                             Fourth layer (μ)                                                                      --  SBC.sub.211                                                                        SBC.sub.242                                                                       --  CH.sub.1                                                                             PB-1(d.sub.2) + a.sub.2                                                               PDC-1                                                                             SBC.sub.11                                    200  200     50     **190   80  50                             Fifth layer (μ)                                                                       --  EVA(a.sub.1)                                                                       Io(E.sub.2)                                                                       --  Io(E.sub.1)                                                                          PP(c.sub.2)                                                                           SBC.sub.321                                                                       EVA(a.sub.2)                                  100  100     100    50      150 40                             Total thickness (μ)                                                                   450 650  600 500 430    560     450 250                            __________________________________________________________________________     Note:                                                                         *Io/Ny.sub.2 = The blended resin having the weight ratio of 70/30             **PB1/a.sub.2 = The blended resin having the weight ratio of 80/20       

The sort of resin:

SBC₁₁ : 80% by weight of EVA(a₁) and 20% by weight of the thermoplasticethylene-α-olefin elastomer (b₁).

SBC₂₁₁ : 70% by weight of EVA(a₂) and 15% by weight of the thermoplasticethylene-α-olefin elastomer (b₁) and 15% by weight of PP (c₁).

SBC₂₄₂ : 70% by weight of EVA(a₂) and 15% by weight of the thermoplasticstyrene-butadiene block copolymer elastomer (b₄) and 15% by weight ofPP(c₂).

SBC₃₂₁ : 60% by weight of EEA (Ethylene-ethylacrylate copolymer, theacrylic acid unit content 13% by weight, MI 1.5, VSP 70° C., MP 89° C.)(a₃) and 20% by weight of the thermoplastic ethylene-α-olefin elastomer(b₂) (α-olefin is butene-1, the butene-1 unit content 13 mol%, saidpolymer is the random polymer, MI 2.0, VSP 52° C., the density of 0.88g/cm³).

PB-1(d₂): The crystalline polybutene-1 (MI 2.0, the density of 0.910g/cm³, the butene-1 unit content 94 mol%, said polymer is modified byethylene. VSP 105° C., MP 110° C.)

PB-1(d₃): The crystalline polybutene-1 (MI 1.0, the density of 0.915g/cm³, VSP 113° C., MP 120° C.)

PDC-1: The vinylidene chloride-vinyl chloride copolymer (the vinylchloride unit content 15% by weight, the plasticizer and the stabilizercontent 2% by weight)

PDC-2: The vinylidene chloride-vinylchloride copolymer (thevinylchloride unit content 20% by weight and the plasticizer and thestabilizer content 1.5% by weight)

PDC-3: The vinylidene chloride-methacrylic acid copolymer (themethacrylate unit content 15% by weight)

CH₁ : The ethylene-acrylic acid copolymer.

CH₂ : The thermoplastic styrene-butadiene block copolymer elastomer(b₄).

Ny₂ : The nylon 6-66 copolymer.

Ny₁ : The nylon 6-10 copolymer.

                                      TABLE 6                                     __________________________________________________________________________                                                     (Comparative                                  Run No.                         Example)                     Characteristics  12  13  14  15  16  17  18  19  d   e                        __________________________________________________________________________    Haze (%)         1.5 1.0 2.1 0.8 1.7 2.2 1.6 2.1 7.6 8.0                      Gloss            150 160 155 152 145 151 142 158 61  52                       Thermal                                                                            20% shrinkage                                                                             58  56  57  60  61  63  65  60  74  77                       property                                                                           temperature (°C.)                                                      80° C. shrinkage                                                                   55  52  48  47  45  40  38  49  27  22                            percentage (%)                                                                Maximum     75  74  77  72  74  73  75  74  60  52                            shrinkage (%)                                                                 Shrink tension (g/mm.sup.2)                                                               240 210 220 230 235 245 210 200 130 80                       Tensile strength (Kg/mm.sup.2)                                                                 12.8                                                                              11.5                                                                              12.0                                                                              12.5                                                                              14.5                                                                              13.1                                                                              13.5                                                                              12.0                                                                              6.5 4.9                      Tensile elongation (%)                                                                         220 240 210 200 205 225 215 230 190 200                      Modulus of elasticity                                                                          25  19  27  22  35  40  37  35  20  27                       on tensile (Kg/mm.sup.2)                                                      Bar-type heat    3.9 4.2 3.8 4.7 4.1 3.7 3.8 3.9 2.1 2.0                      sealing strength (Kg/15 mm width)                                             O.sub.2 permeability (cc/m.sup.2 · day · atm)                                45  40  20  42  40  47  31  19  47  56                       Film thickness (μ)                                                                          42  58  55  45  40  51  41  44  71  69                       __________________________________________________________________________

Note

The comparative sample (d) is the shrink bag for wrapping the raw meat,it comprises the barrier layer of vinylidene chloride of about 10μ inthickness and EVA layer [the vinylacetate unit content 15% by weight,said layer is cross-linked with the radiation of energy ray (the gelcontent: 72% by weight)] having 46μ in thickness as the inner layer andthe EVA layer (the VAC unit content 15% by weight) having 15μ inthickness, these layers are stretched at 97° C.

The comparative sample (e) comprises the EVA layer (the VAC unit content15% by weight), the PDC₁ layer, the EVA layer (the VAC unit content 18%by weight) and the ionomer (E₁) layer having 19/10/5/35μ in thicknessrespectively. This four layer film was stretched at 92° C.

The drawing films of Run Nos. 12-19 had the high dart impact strength ofmore than 90 Kg.cm, while the comparative samples (d) and (e) had 39 and38 Kg.cm respectively.

Each of the sample Run Nos. of the present invention was remarkably goodin the optical property, the low temperature shrink property, the shrinktension, the tensile strength, the impact strength, the sealingstrength, and the barrier property in comparison with the commercialwrapping film (d). The practical wrapping test was carried out bywrapping 10 Kg of the raw meat under vacuum and then passing it in theshower of hot water of 85° C. for 3 seconds thereby obtaining the goodwrapping finish tightly fitted with goods which was superier in thestorage life.

The gas (O₂) barrier property was measured after bending the comparativefilm (d) by hand so as to form the wrinkle on the surface of the film.From the test result, the pinhole was formed and the gas barrierproperty was depressed to 95 cc/m². day.atm. In the comparative film(e), the said value was remarkably depressed to 120 cc/m².day.atm. Whilein the film of Run No. 16, the said phenomenon was not observed.

EXAMPLE 5

The raw tubular film was manufactured using the various sort of polymersand the combination of layers under the condition of Table 7 accordingto the process of Example 4.

                                      TABLE 7                                     __________________________________________________________________________    Combination in                                                                           Run No.                                                            thickness of raw film                                                                    20  21  22  23  24  25   26  27* 28**                              __________________________________________________________________________    First layer (μ)                                                                       PP(c.sub.1)                                                                       Ny.sub.2                                                                          PP(c.sub.1)                                                                       PP(c.sub.1)                                                                       PET.sub.1                                                                         PP(c.sub.1)                                                                        PP(c.sub.1)                                                                       PP(c.sub.1)                                                                       PP(c.sub.1)                                  6   6   10  10  5   10   5   10  5                                 Second layer (μ)                                                                      SBC.sub.11                                                                        SBC.sub.211                                                                       SBC.sub.211                                                                       SBC.sub.321                                                                       PB.sub.1                                                                          PB.sub.1                                                                           SBC.sub.011                                                                       SBC.sub.111                                                                       SBC.sub.113                                  188 180 180 180 20  40   190 180 140                               Third layer (μ)                                                                       PP(c.sub.1)                                                                       Ny.sub.2                                                                          PP(c.sub.1)                                                                       PP(c.sub.1)                                                                       SBC.sub.211                                                                       SBC.sub.411-2                                                                      PP(c.sub.1)                                                                       PP(c.sub.1)                                                                       PB.sub.1                                     6   6   10  10  150 100  5   10  50                                Fourth layer (μ)                                                                      --  --  --  --  PB.sub.1                                                                          PB.sub.1                                                                           --  --  PP(c.sub.1)                                                  20  40           5                                 Fifth layer (μ)                                                                       --  --  --  --  PET.sub.1                                                                         PP(c.sub. 1)                                                                       --  --  --                                                           5   10                                             Total thickness (μ)                                                                   200 192 200 200 200 200  200 200 200                               __________________________________________________________________________     Note                                                                          *The film was treated with the radiation of the high energy ray of 7 Mrad     The gel content of the SBC layer was 7% by weight.                            **The film was treated with the radiation of the high energy ray of 10        Mrad. The gel content of the SBC layer was 38% by weight.                

The stretching was carried out at the temperatures of 35° C., 48° C.,36° C. and 38° C. in the films of Run Nos. 20-23 respectively, while atthe temperatures of 50° C., 35° C., 32° C., 33° C. and 35° C. in thefilms of Run Nos. 24-28 respectively.

The resulted films had good properties as shown in the Table 8.

                                      TABLE 8                                     __________________________________________________________________________                  Run No.                                                         Characteristics                                                                             20  21  22  23  24  25  26  27  28                              __________________________________________________________________________    Haze (%)      0.8 0.5 0.7 0.7 0.6 0.8 0.7 0.8 1.0                             Thermal                                                                            20% shrinkage                                                                          58  64  56  60  72  55  58  59  57                              property                                                                           temperature (° C.)                                                     Maximum  75  71  78  76  70  76  75  81  82                                   shrinkage (%)                                                                 Shrink   220 180 240 215 220 210 165 260 250                                  tension (g/mm.sup.2)                                                     Tensile strength (Kg/mm.sup.2)                                                              14.1                                                                              15.2                                                                              14.1                                                                              13.8                                                                              16.2                                                                              13.8                                                                              11.9                                                                              13.2                                                                              17.0                            Tensile elongation (%)                                                                      170 150 200 165 180 210 200 165 150                             Modulus of elasticity                                                                       40  50  37  46  49  40  36  48  42                              on tensile (Kg/mm.sup.2)                                                      Dart impact strength                                                                        32  45  33  35  40  47  34  41  49                              (Kg · cm)                                                            Heat seal strength                                                                          2.1 --  2.1 2.5 --  2.2 2.1 2.4 2.0                             (Kg/15 mm width)                                                              Film thickness (μ)                                                                       16  17  17  16  16  16  16  15  15                              __________________________________________________________________________

Note

1. The sort of the SBC layer

SBC₄₁₁₋₂ : 50% by weight of EMMA (the methyl methacrylate unit content17% by weight, MI 1.7, VSP 73° C., MP 87° C.) (a₄), 30% by weight ofethylene-α-olefin elastomer (b₁), 10% by weight of PP (c₁) and 10% byweight of HDPE (the polymer is copolymerized with 2 mol% of propylene,MI 1.0, the density of 0.96 g/cm³, VSP 129° C., MP 123° C.) (c₃).

SBC₀₁₁ : 75% by weight of ethylene-α-olefin elastomer (b₂) and 25% byweight of PP(c₁).

SBC₁₁₃ : 70% by weight of EVA (a₁), 20% by weight of theethylene-α-olefin elastomer (b₁) and 15% by weight of HDPE (c₃).

2. The sort of another layer

PET₁ : The thermoplastic polyester resin.

EXAMPLE 6

The raw tubular film was manufactured using the various sort of polymersand the combination of layers under the condition of Table 9 accordingto the procedure of Example 5.

                  TABLE 9                                                         ______________________________________                                        Combina-                                                                      tion in                                                                       Thickness                                                                             Run No.                                                               of raw film                                                                           29       30       31     32     33                                    ______________________________________                                        First   PB-1(d.sub.1)                                                                          EVA(a.sub.1)                                                                           EVA(a.sub.1)                                                                         Ny-1   EVA(a.sub.1)                          layer (μ)                                                                          140      20       10     30     20                                    Second  EVA(a.sub.1)                                                                           PB-1(d.sub.1)                                                                          EVA(a.sub.2)                                                                         PB-1(d.sub.2)                                                                        PB-1(d.sub.1)                         layer (μ)                                                                          60       160      5      110    130                                   Third   --       EVA(a.sub.1)                                                                           PB-1(d.sub.3)                                                                        Io(E.sub.1)                                                                          Io(E.sub.2)                           layer (μ)     20       130    30     50                                    Fourth  --                EVA(a.sub.2)                                                                         Ny-1                                         layer (μ)              5      30                                           Fifth   --                EVA(a.sub.1)                                        layer (μ)              30                                                  Total thick-                                                                          200      200      180    200    200                                   ness (μ)                                                                   ______________________________________                                    

The stretching was carried out at the temperature of 35° C., 40° C., 32°C., 45° C. and 38° C. in the films Run Nos. 29-33 respectively. Thestretching was carried out stably and the characteristic properties ofthe resulted films were shown in Table 10.

                  TABLE 10                                                        ______________________________________                                                   Run No.                                                            Characteristics                                                                            29      30      31    32    33                                   ______________________________________                                        Haze (%)     2.4     0.9     0.5   0.5   1.1                                  Ther- 20% shrink-                                                                              56      58    53    65    55                                 mal   age temper-                                                             prop- ature (°C.)                                                      erty  Maximum    80      83    82    80    78                                       shrinkage                                                                     (%)                                                                           Shrink     200     290   320   270   260                                      tension                                                                       (g/mm.sup.2)                                                            Tensile strength                                                                           12.1    13.5    15.1  14.7  12.1                                 (Kg/mm.sup.2)                                                                 Tensile elonga-                                                                            145     165     200   175   125                                  tion (%)                                                                      Dart impact strength                                                                       27      32      45    40    34                                   (Kg · cm)                                                            Heat seal strength                                                                         2.2     2.3     2.1   1.7   2.4                                  (Kg/15 mm width)                                                              Film thickness (μ)                                                                      18      18      15    20    18                                   ______________________________________                                    

EXAMPLE 7

The raw tubular film was manufactured using the various sort of polymersand the combination of layers under the condition of Table 11 accordingto the procedure of Example 5.

                  TABLE 11                                                        ______________________________________                                        Combination in                                                                              Run No.                                                         thickness of raw film                                                                       34       35       36     37                                     ______________________________________                                        First layer (μ)                                                                          SBC.sub.111                                                                            SBC.sub.111                                                                            SBC.sub.111                                                                          SBC.sub.111                                          140      120      120    120                                    Second layer (μ)                                                                         Io(E.sub.1)                                                                            PB(d.sub.1)                                                                            PDC-1  PDC-1                                                30       50       100    50                                     Third layer (μ)                                                                          Ny.sub.1 EVL-1    Io(E.sub.1)                                                                          EVL-l                                                100      30       30     30                                     Fourth layer (μ)                                                                         Io(E.sub.1)                                                                            PB(d.sub.1)                                                                            Ny.sub.1                                                                             Io(E.sub.1)                                          30       50       50     30                                     Fifth layer (μ)                                                                          SBC.sub.111                                                                            SBC.sub.111                                                                            SBC.sub.111                                                                          SBC.sub.111                                          300      250      200    200                                    Total thickness (μ)                                                                      600      500      500    430                                    ______________________________________                                         EVL-1: 99% saponificated EVA (ethylene content: 40 mol %)                

                  TABLE 12                                                        ______________________________________                                                       Run No.                                                        Characteristics  34      35      36    37                                     ______________________________________                                        Haze (%)         1.3     1.2     1.4   1.4                                    Thermal                                                                              20% shrinkage 65      59    60    58                                   property                                                                             temperature (°C.)                                                      Maximum shrinkage                                                                           69      72    71    73                                          (%)                                                                           Shrink tension                                                                              190     220   200   210                                         (g/mm.sup.2)                                                           Tensile strength (Kg/mm.sup.2)                                                                 17.5    12.8    15.8  13.5                                   Tensile elongation (%)                                                                         160     150     180   170                                    Dart impact strength                                                                           not less                                                                              not less                                                                              not less                                                                            not less                               (each thickness) (Kg · cm)                                                            than 90 than 90 than 90                                                                             than 90                                Strength of bar sealing                                                                        4.2     3.3     2.9   3.1                                    (Kg/15 mm width)                                                              O.sub.2 permeability                                                                           55      5       20    2                                      (cc/m.sup.2 · day · atm)                                    Film thickness (μ)                                                                          50      42      40    37                                     ______________________________________                                    

The stretching was carried out at the temperatures of 46° C., 48° C.,39° C. and 42° C. in the films Run Nos. 34-37 respectively. Thestretching was carried out stably and the characteristic properties ofthe resulted films were shown in Table 12.

Each of the sample Run Nos. of the present invention was remarkably goodin the optical property, the low temperature shrink property, the shrinktension, the tensile strength, the impact strength, the sealing strengthand the barrier property in comparison with the commercial wrapping film(d).

The practical wrapping test was carried out by wrapping 10 Kg of the rawmeat with the film of Run No. 35 under vacuum and then passing it in theshower of hot water of 85° C. for 3 seconds thereby obtaining the goodwrapping finish tightly fitted with goods.

COMPARATIVE EXAMPLE 1

The raw tubular films having the combination of Table 13 were extrudedaccording to the process of the above mentioned Example.

                                      TABLE 13                                    __________________________________________________________________________    Combination                                                                   in thickness of                                                                         Comparative Run No.                                                 raw film  5  6  7  8  9  10 11  12  13  14  15  16                            __________________________________________________________________________    First layer                                                                             a.sub.1                                                                          b.sub.1                                                                          c.sub.1                                                                          a.sub.1                                                                          Ny.sub.1                                                                         c.sub.1                                                                          a.sub.3                                                                           a.sub.1                                                                           a.sub.3                                                                           2.sub.1                                                                           PDC-1                                                                             PDC-1                                   200                                                                              100                                                                              200                                                                              100                                                                              10 50 60  80  40  100 300 300                           Second layer       b.sub.1                                                                          a.sub.1                                                                          b.sub.1                                                                          PDC-1                                                                             Io(E.sub.1)                                                                       b.sub.1                                                                           PDC-1                                                                             a.sub.1                                                                           PP.sub.1                                         50 130                                                                              100                                                                              80  10  10  50  100 100                           Third layer        c.sub.1                                                                          Ny.sub.1                                                                         c.sub.1                                                                          a.sub.3                                                                           EVL-1                                                                             PET a.sub.1                                                  100                                                                              10 50 60  30  30  50                                    Fourth layer                    Io(E.sub.1)                                                                       a.sub.3                                                                   10  30                                        Fifth layer                     a.sub.1                                                                           Io(E.sub.1)                                                               70  40                                        Total thickness (μ)                                                                  200                                                                              100                                                                              200                                                                              200                                                                              150                                                                              200                                                                              200 200 150 200 400 400                           Stretching (°C.)                                                                 20 20 20 20 20 20 20  20  20  20  20  20                            temperature                                                                             150                                                                              100                                                                              150                                                                              150                                                                              100                                                                              100                                                                              100 100 100 100 100 100                           __________________________________________________________________________     Note: a.sub.3 was EVA (VAC content 6% by weight (2.1 mol %), MI 0.9, VSP      79° C., MP 102° C.).                                       

As the result, the film of the comparative sample Run No. 5 could not bestretched at all at the temperature in the range of 20 to 130. At thestretching temperature of 20°-80° C., the film was inflated to someextent and sustained puncture thereby restoring in its former condition.And at the stretching temperature of 140° C., the film was stretched toa film 13μ in thickness with difficulty. This film had Haze of 6.8%, the20% shrinkage temperature of 120° C., the shrink tension of 3 gr/mm²,the tensile strength of 2.1 Kg/mm², the elongation of 490% and the dartimpact strength of 5 Kg.cm. These characteristic properties weredifferent from those of the present invention.

The film of the comparative sample Run No. 6 could not be stretched atall even at the temperature of 100° C. and sustained puncture. The rawfilm was apt to cause the brocking and to become soft and sticky.

The film of the comparative example Run No. 7 could not be stretched atall at the temperature of 20°-130° C. and sustained puncture and at thetemperature of 145° C., the film could be very unstably stretched withdifficulty. However, the resulted film had the same extent of thecharacteristic properties to those of the commercial PP shrink film.

The film of the comparative sample Run No. 8 could not be stretched andmerely sustained puncture at the temperature of 20°-130° C. and at thetemperature of about 150° C., the film could be stretched with theunstable state. This film was whitish and easily broken. There wasmerely obtained the film having the bad optical property of Haze 6.2%.

The films of the comparative samples Run Nos. 9 and 10 could not bestretched at the temperature of 20°-100° C.

The film of the comparative sample Run No. 11 could be somewhat inflatedby blowing the compressed air into the raw tubular film at the beginningof blowing but sustained puncture. The film could not be continuouslystretched. And at the stretching temperature of 130° C., there wasmerely obtained the whitish and ill-balanced film having the largepartiality in thickness in small quantities. This film sustainedpuncture.

The films of the comparative samples Run Nos. 12 and 13 could not bestretched at the temperature of 20°-100° C. and sustained puncture.

The film of the comparative sample Run No. 14 was stretched aftertreating it with the energy ray (electron ray) of 5 Mrad, but the filmcould not be stretched and sustained puncture. At the temperature of140°-150° C., this film could be stretched to the film 15μ in thickness.This film had Haze of 7.5%, the 20% shrinkage temperature of 115° C.,the shrink tension of 20 gr/mm², the tensile strength of 2.8 Kg/mm², theelongation of 39%, the dart impact strength of 8 Kg.cm and the O₂-barrier property of 150 cc/m².day.atm. These characteristic propertiesof this film were inferior to those of the film of the presentinvention.

The film of the comparative sample Run No. 15 could be somewhat inflatedlike the bubble at the beginning of blowing but sustained puncture.

The film of the comparative sample Run No. 16 sustained puncture at thebeginning of stretching and the test piece could not be obtained.

What is claimed is:
 1. A process for manufacturing a multilayered filmincluding at least one layer preponderantly containing a cold-drawableresin selected from the group consisting of blended and unblendedspecific polymers, [1] (B)+(A)+(C), [2] (B)+(A), [3] (B)+(C), [4] (D),and (5) (E), wherein,(A) is at least one ethylene type polymer selectedfrom the group consisting of copolymers of ethylene with other monomerssuch as vinyl esters, aliphatic unsaturated carboxylic acids and alkylesters of said carboxylic acids, ionically crosslinked resins derivedfrom said copolymers and low-density polymers of ethylene, (B) is a softcopolymer elastomer having a Vicat softening point of not more than 60°C., (C) is at least one polymer selected from the group consisting ofcrystalline polypropylene, high-density polyethylene, crystallinepolybutene-1 and polymethyl pentene-1, (D) is a crystalline polybutene-1having a concentration of 50 to 100% by weight, and (E) is an ionicallycrosslinked resin, said multilayered film consisting of(I) at least onecold drawable resin layer (CDR) and at least one layer (Br) formed of apolymer possessing an O₂ barrier property; (II) at least one colddrawable resin layer (CDR), at least one layer (Br) formed of a polymerpossessing an O₂ barrier property and at least one layer (S) formed ofat least one polymer selected from the group consisting of crystallinepolypropylene, polyethylene, ethylene-vinyl acetate copolymer,ethylene-aliphatic unsaturated carboxylic acid copolymers andethylene-aliphatic unsaturated carboxylate copolymers; (III) at leastone cold drawable resin layer (CDR), at least one layer (Br) formed of apolymer possessing an O₂ barrier property and at least one layer (S) andat least one adhesive layer (AD) formed of one member selected from thegroup consisting of ethylene-vinyl acetate copolymer, ethylene-α-olefincopolymer elastomers, ethylene-aliphatic unsaturated carboxylic acidcopolymers and derivatives thereof, and block-copolymerized elastomersof styrene-conjugated diene type monomers, or (IV) at least one colddrawable resin layer (CDR), at least one layer (Br) formed of a polymerpossessing an O₂ barrier property and at least one adhesive layer(AD);comprising: extruding the cold drawable resin into a molten sheetand then quenching said sheet to solidify; preparing a multilayered rawfilm having, as at least one of said layers therein, said solidifiedcold drawable resin sheet; and cold drawing said multilayered raw filmat a temperature between 20° C. and 80° C., provided that the drawingtemperature is not exceeding the Vicat softening points of the specificpolymers [1], [2], [3], [4] and [5], to yield a drawn film having anarea between 3 and 30 times greater than said raw film.